i was looking for help on what this condition may be...

okay my bro is 16, and he as a mild intellectual disability so the doctor says but this was also about 3 years ago this was diagnoised.... he has symptoms including..

- mood swings usually angry try's to fight people
- says he hears voices telling him caca
- you hear him whispering things back to himself under his breath like hes talking to somebody? or repeats words/things oveer and over
- antisocial, try's to avoid people, doesn't want to make friends
- hits my mother when he don't get his way
- never cleans after himself, rooms a mess, doesnt put things away
- appearance issues cutting his hair
- no sucidal issues, brought it up a few times but thats rare
- thinks hes fat when hes only 125lbs, and myself and my friends have proved to him he isn't fat if he weighs less then us two girls included (were only 19) our highest was 150.... he used to be 180 but kids made fun of him.
- he avoids sitting down, he thinks if he sits its for lazy people and he will get fat, hes avoiding many foods, and he'll just pace around the house with a hoodie on, a coat, and shoes, like hes always going somewhere, he will walk after every meal for about an hour like hes trying to sweat it out or something, i honestly don't know what to do with his kid? we took him to like 3 different doctors, and all they have to say is there is "nothing wrong with him" i questioned my mom that ikes to think nothing of it but knows there is a problem, she doesnt think its serious and he'll grow out of it, but recently its only been worse and shes the type of person who likes to push everything off, i and my girlfriend think all this caca is very unusual and not how a 16 year old should act.... but the funny thing is, at school hes doing fine, and passing all his classes??? we were thinking its more of..

skitzophrenia
start of anorexia

but not sure, what do you guys think? theres so much and its starting to drive everyone around him crazy just by putting up with him!!