What is wrong with me?

You sound exactly how I was when I was 14. I was quiet, full of fear at times, prone to occasional outbursts of anger toward people, shying away from social occasions to the point when my school friends came to visit my house, I'd go up into my room & ignore them, leaving my brother to entertain them! And mood swings, I was up & down like a yo-yo! My only advice to you is to see your doctor please. For your own sake. I was bottling up a lot of things that was going on at home at that time which seriously affected how I thought & felt within myself. I don't know if the same is going on with you but please see your doctor anyway & have an honest chat with him or her. It may just be a mood disorder which can be treated with medication.