I agree on the overwatering suspicion. Buy one of those moisture meters at walmart, they look like this and are only about 4 bucks. They aren't always fool proof, but it gives you an idea of how wet or dry your soil really is down there below the surface. In my home, my peace lily usually gets watered once every 5 days on average. It really varies, I have a smaller variety peace lily compared to yours. Secondly -- fertilize healthy plants. If a plant isn't doing well, you need to get it healthy first before fertilizing it. And make sure it's a weak fertilizer, don't use too much. For repotting, you could simply lift it out of the pot, try and shake off the soil and inspect the roots. If the roots aren't white and they are brown and mushy, that's root rot. You could cut out the bad roots and try replanting in new soil. Drainage is important, so you want a pot with a hole in it and a well draining soil (if you're just using standard houseplant potting mix, you could throw some perlite in to aide in drainage). Watering -- In the future, watch your watering. You'll definitely kill plants like this if you water everyday, even every other day. All plants need to be watered when they need it, not based on a weekly or every X days schedule. A moisture meter will help with that. Finally, don't let the water go from your kitchen sink to the plant. If you water using tap water, let the water sit for at least a day to allow chlorine and anything else the plant won't like to evaporate from the water. And you want it to be room temperature or slightly warmer, not cold water that will shock the plant. I like to fill up a gallon jug of water, let it sit out without a lid for a couple days, then i just put the lid back on and leave it on my fridge. Anytime I need to water, I just use that.

I have used the same model for a couple years now. I generally use Leso products, (more pelletized than Scotts..But I generally run 5-7 ft apart, most of the ferts I set the spreader at 14-15. Earthway's web site has a settings chart if you look up the model. Lesco also has the settings for their ferts if you look on "spreader settings" Its a good spreader and spreads very evenly for the price Dan T

Bishop weed is notoriously difficult to kill, so go industrial with your smother, like multiple layers of cardboard, a thick, heavy layer of mulch to hold it firmly against the soil. A few sheets of newspaper won't do the job on that one. The benefit of using something that will decompose is that it doesn't have to be removed, and is not impermeable to moisture penetration. It will also conform to every groove and dip in the soil surface, which blocks the light completely, and the air and the very space needed for leaves to grow. (Starting a new planting area this way fits under the "lasagna" umbrella of methods.) I might use the smothering to eliminate mowing all the way to the corner, looks tight between the lilac and house. Then use some kind of border, bricks or landscape timbers, to keep the grass separated from that area. Next year, check under the smother. If you find no signs of life, you should be able to add some other plants there, whatever perennials, annuals you might like in your new flower bed. Just make sure to make the holes all the way through the cardboard if it has not fully decomposed. My concern about the light wasn't from the amount of it visible in the pic, but from the combination of things surrounding it, the structure of the lilac, and that it looks like it's to the north of the house/other shrubs, and under the eave from that angle. If you start new shrubs with pieces trimmed from this one, you could put them in other spots that get more light, to have some great lilacs since this one is in a less than optimal spot. Not an unattractive plant, just not able to fully perform there. Everybody does not do it the same way, have the same opinions or goals, so definitely take the info and use it to make your yard the way you like it. That looks like the same kind that makes a great tree, although commonly sheared into a shrub or hedge.

I bet the plant is very stressed out after being repoted 3 times in such a short time frame. If the roots are rotting your overwatering it. Were any of the roots white when you repotted it last time? It may be beyond saving and if you don't want to go through the effort to revive it, it'd be best to just get a new one and care for it properly from the beginning....