I'm sorry you feel that way bro, I was there about eight years ago when I was in high school. In my case though the depression came from taking Acutane for acne, but the result was a very depressed outlook on life, unwilling to socialize, spending six hours a day just napping (I'd go to school, come home, nap, eat dinner, do a little homework and then go to bed).
One small pattern I've noticed both with myself when I was depressed and with friends who are/were in the same boat is they would shut themselves into their apartment/house/room. Sometimes, and this may sound silly, but just getting a larger than normal dose of fresh air can help a lot. You said you do or did bodybuilding so I imagine you would workout inside a gym, maybe switch it up and take a walk regularly or even a bike ride? It seems like sometimes cardio does a better job of releasing endorphins than lifting, but that may just be me. I know if I'm feeling a bit low on a particular day things turn around a bit when my wife and I take a stroll down the bike path near our place.
My wife and I have a friend with a gastrointestinal disease and sadly I could probably count the number of times this friend has left their home on two hands. I honestly think the stale air and dark lighting that comes from always being inside can really have an emotional and psychological impact on a person.
Sorry if I'm way off the mark here, I'm not yet Orthodox so I don't know near as much as our friends here that are, thus I can't really make any book recommendations. I'll be praying for you though, I can somewhat relate by experience how rotten depression can be.