Can you get any photos of him? It honestly sounds like you added way too many fish at once. Either stress or ammonia overload could have kicked in whatever is wrong with him and sent it into high gear. Sorry you're having problems with him.
again i will mention that i noticed he was thin and different when i got him. its only now that i really noticed as i thought he would fattern up. I cant get any pics because dad wont let me use his camera