I have social anxiety and a high degree of shyness towards anyone. How to relieve?

Sometimes I wish to stay locked up in my apartment watching TV and movies for several days like I did in undergrad. I did not go out much, but now that I am in medical school, I have to go to class, and the library to study. But I can't talk to people. I feel so inferior to everyone. I don't consider myself a human like other humans, I am just not worth talking to or having any sort of relationship. I mean it is completely unthinkable for someone to actually like me, since I don't like myself. I have just a shred of confidence for daily sustenance, just to walk around and respond to what others say, or sometimes to start a conversation which is boring. I probably look like the most stuck up person on the planet, since I am so serious all the time and don't smile. But I am afraid to smile, afraid to open up to others. I see myself as a defense, a shield. Solitude is painful but not as painful as being hurt by someone you trust in. That just makes you feel like an idiot, a dog. I have never had real friends, nor a girlfriend. I only have my family to depend on, but they can't help me. All they tell me is to look at the positives, that I am brilliant, kind and fair to others, naive, caring for those I love. I started to exercise a few weeks ago everyday, but I have not felt much change in my attitude. I have been bullied a lot in my childhood, for about 2-3 years. I don't have a close relationship with my dad since he like to point out my flaws when he has some tension in his mind. When he is back to normal, I don't want to like him because it would just hurt to have relations. Why does everyone have something else on their mind, some motive, betrayal scheme, or undercurrent? I can't figure out how to help myself out of this vicious cycle.