Have you considered that it might be the characteristics of the type of orange? There are quite a few 'sour orange' varieties out there. That would be my first thought, since you mentioned that the tree always produces sour fruit.

You have at least 3 pests maybe 4 #1 Citrus Leaf Miner- It is suggested not to treat mature citrus trees for this pest #2 Cottony Cushion Scale- You may not need to treat for it if you can find some vedalia beetle #3 Ants- They seem to be going after the excretion from the scale so if you get rid of the scale they should also go away. #4 You may also have mealybugs. It was a little hard for me to tell from those pictures as they can sometimes be similar to the scale. Someone here may be able to better tell than I. This website that follows gives a good explanation about most citrus pest and how or when to treat them. It also has good pictures to aid in identifying them. Here is a link that might be useful: helpful citrus site

Hey guys! Just an update. Once my lemon started showing new shoots near the bottom of the plant I chopped it back. I cut off many of the weird sideshoot branches, anything that wasn't vertical pretty much. I left it with one main "trunk" branch and several smaller ones, now mostly without mature leaves. It just can't be so big inside and I figured if I kill it, I kill it, but the chop had to happen. A four foot plant just wasn't happening inside the apartment. It's been sitting in a foil lined cardboard closet with its own huge grow light. Once per week I've been drenching it in the shower and giving some Foliage Pro. I figured one it leafs out I can put it on the grow table with the other plants. Holy Hannah, this tree is *exploding* with growth. There isn't a single branch that isn't now pushing out new growth, new leaves. Every day I look there is more than the day before, and it's all growing SO fast. And, on top of that - FLOWER BUDS! On one of the only branches left that has any mature leaves (one of the few that didn't get chopped!) it pushed out a few flowers! I am SO EXCITED, it's been a long time and I feel like it's a testament to how much I've learned to keep this guy alive. I hope some of the new branches grow a few flowers to go along with the leaves! It's been years since it's flowered, and with half the plant chopped down (more than half?) it should have plenty of energy to produce new leaves and a few fruit. It's amazing how fast these plants grow. The flower buds were not there two days ago! Here's some pictures, one of some of the new growth along the bare chopped branches and one of the buds! (I wish the branches would grow some leaves instead of new branching but I'll take what I can get!)

this my plant. Sorry for the bad pic. Lol thanks John. It's in a South facing window which gets at least 6 hrs direct light. The fertilizer is one my we got that was made for citrus trees. It gets fed monthly. Thanks for the help and let me know if I need to do anything different.