St Augustine needs a very specific herbicide so you don't kill the St Aug. I'm not familiar with Scott's products for southern lawns, but, as neilaz said, use a fertilizer to fertilize and a liquid herbicide to spot spray weeds. But contrary to what neilaz said, Weed B Gone is not the product. It will kill St Aug. Weed B Gone is great for any other grass; just not St Aug. No, St Aug will not crowd out broadleaf weeds. It will do a pretty good job with bermuda but some other grassy weeds give it trouble. You are in luck, though, there is a very effective herbicide. This one DANG. I didn't realize that picture was that huge!! If you use it right (shake first and then spray as a mist) it works very well. If you use too much the St Aug will yellow for a week or so before coming back. But the weeds will not come back. When the weeds die out, you can buy a few flats of St Aug and scatter them around in the bare spots. Keep them watered well for the first 3 weeks until the roots knit in with the underlying soil. Then start to back off. Use organic fertilizer like alfalfa pellets (rabbit chow) heavily and the St Aug will spread about 5 feet in all directions. Then in the fall after the hot weather is over, it will spread another 5 feet in all directions. You should have pretty good coverage, if not density, by November. Then next year the density will catch up due to the spreading in among itself. Key is to never let it dry out. St Aug does not go dormant like some other grasses. When it dries out it goes straight to dead. Water it deeply and infrequently. Deeply means a full inch all at one time. Infrequently means monthly in the winter transitioning to weekly in the hottest heat of summer. If you have particularly dry and windy days that evaporate the water more quickly, you might have to go to a 5-day schedule. Once the grass is established, there is never a case where you should water daily for a few minutes at a time. I use an oscillator type sprinkler - the new turbine drives, not the old mechanical linkage. These things are great. They provide a very slow application. Mine takes 8 full hours to get an inch of water. Your timing will vary depending on humidity, wind, soil type, grass height, shade, clouds, and temperature. Oh and raise your mower all the way to the highest setting for St Augustine. It looks much more plush and needs much less water. I have a St Aug experiment going on. It has not been mowed since October of 2011. In some places the grass height is 30 inches. And in those places it has not been watered since Oct 2011. Here is a pic of that. Yes I know...pretty funny to see St Augustine that tall. It's an experiment, not neglect. Notice there are no weeds either. My yard is surrounded by weeds, so that is one of the results of the tall grass experiment.

I might seem brutal but I'm going to be frank. Some of what you did is "wrong," by the general consensus of GardenWeb writers over the years. Here goes... 1. I've manually pulled large amounts of dandelions and other weeds with a long steel weed puller. I'd say I've filled about two of those roll out to the curb trash bins completely with pulled weeds. However, this may be a losing battle as there's still a large amount of weeds still sprouting up. I've gotten most of the bigger ones, though. The weed puller is good for dandelions but not for clover or henbit. My hanbit has amazingly weak roots but yours had taproots from heck. Hmmmm? 2. Because of the losing battle, I talked with a person at Home Depot and they suggested using weed and feed. I applied that to the lawn and I gotta say, I don't think it did anything. There were still just as many weeds a week later and I don't see and dead or dying ones. I started doing some research on-line about weed and feed and it seems like it may be some pretty nasty stuff and I may not use it again as I have a 2 year old daughter at home. Your experience is exactly what we read here year after year. As you have spent the money and learned, Weed N Feed doesn't work. Weed killing and grass feeding work best when done as separate tasks. Fertilize first and spot spray for weeds using Weed B Gone about 2 weeks after fertilizing. The weed plants die best when they are growing well after being fertilized. Now is a good time to fertilize. The grass will thicken up and then in early June you can spot spray the individual weeds. Clover and henbit should die quickly or after a second spraying. Crabgrass is probably best to let live this one last season. 3. I recently just had the lawn aereated. A better time to aerate is in the fall, but really there was no harm done. 4. After the lawn was aereated I went out and threw grass seed down on the bare patches. No harm there either but not much benefit either. Grass seed will not sprout unless it gets continual moisture for a couple weeks. That means it needs a short drink of water three times a day, every day. Not coincidentally, crabgrass seeds need exactly the same care to sprout. This is one reason why seeding in the spring does not give you the results you expect. If you seed in the fall, crabgrass is dying about then. Follow bpgreen's suggestions for watering and mowing for this one last season. Ignore any crabgrass or grassy weeds you have until September. Fighting it now is a losing battle and is just frustrating. But I disagree with him that you have Kentucky bluegrass. Why? Because if you did it should be much thicker. I've certainly been wrong guessing grasses from pictures, but I guess my point is that if you get a good Kentucky bluegrass going this coming fall, even with modest neglect it should get nothing but better and better in the coming years. Yours is getting worse and worse. That is what fescue does when it is neglected. If you want it to look better and better, then I would suggest killing with something after the summer heat breaks. That day/time is different everywhere so I can't pick a date for you but I'd guess it would be late August or early Sept. The idea would be to kill it with something like RoundUp, wait a week and spray anything that did not die the first time, remove all the dead grass with a power rake and leaf blower, spot-fill any low spots you want fill, scatter the best Elite Kentucky bluegrass seed you can afford (not available at Walmart), roll that seed down with a water filled roller, and water it daily like I outlined above for 10-15 minutes, three times per day. When it sprouts, set your mower for 3.25 inches and mow when the grass gets tall enough. Fertilize after you have mowed two times. Fertilize again on Thanksgiving. Next year fertilize on Memorial Day, Labor Day, and Thanksgiving. Next year it will seem to sleep, the following year it will creep, the third year it will leap out of the ground like it's on rocket fuel.

This is a close up of the clover patches and grass mixed in

Grass needs lots of sun to look good. There is no chance of having a decent lawn with all that shade. You may want to try and put in a shade loving garden to improve the look of your yard.