Why do I fear intimacy?

I really really feel uncomfortable with just about any kind of touch. When I see a friend or family member about to hug me I tighten up and bear it and if they catch me off guard I go completely stiff and abruptly pull away. When someone goes to high five me or shake my hand I "fist pound" them instead laughing it off like "oh I'm too cool for high fives". When someone drapes their arm around my shoulders or grabs my waist or anything like that, if I'm really comfortable around them I'll pull away, and if I'm not so close with them I will stand stiff as a board and not talk. Even if I'm sitting next to someone and their leg accidentally touches mine I pull away like it's on fire and my nerves electrify. All of this is intensified dramatically with men. I'm 18 and I've never had a boyfriend or even close boy friends. I become so uncomfortable with guys but I try not to let it show. I'm not a germaphobe and my mom has not neglected me. I've seen my dad a few times a month since they split up when I was five but I don't respect him so his absence in my life has never affected me. I hate emotional intimacy as well. I freak out when people try to get in my head. In elementary school and jr high i would lash out at guidance counselors because i felt as though they were trying to see my private thoughts. One more thing is when a guy likes me and i like him i become blunt and mean. Before i wouldve been feminine and fun but as soon as i feel as though something could happen i become awkwardly rude and almost robotically monotone and boring. What is wrong with me and how can I fix it?