Why can't I get into sex

I lost my virginity at 16 and it didn't feel good. I don't think the person did anything wrong. It's just I didn't feel like sex was something I liked. I thought maybe it was just bad sex. I'm 24 now and I've been with a few people. Boys and girls and I've never once was the one to start sex. I just don't really like it. I thought once I found someone and fell in love then I would like sex. I have a boyfriend of 3 years who I am extremely in love with and we just started having sex... And... Nothing... I don't like sex. I don't crave sex. I don't want sex. And its not fair to my boyfriend who waited so long and obviously wants to have sex. What is wrong with me? How can I fix me?