Worried about my sons mental health?

He is 16 and gets frequent moodswings.He will be one minute happy and talkative and the next he is angry or upset.Just talking to him can cause him to get very angry. He doesnt like people touching him and prefers to be by himself.With friends he is full of jokes and smiley but he has said that he feels that is 'not really him'.He likes to know whats going to happen and it sort of distresses him when it changes, for example if we planned to go out somewhere at the weekend and then it changes at last minute he gets irritated and moody. Also he sometimes rocks back and forth, it seems to be subconscious as he doesnt always realise he is doing it until it is pointed out however he also does it consciously when he is upset as he says it makes him feel better. He struggles with social situations and cannot maintain eye contact when talking to people. he does not have any diagnosed learning or behavioural disorders, is not involved with drugs and his school work is above average. Any advice?