I wouldnt worry about it if I were you. I'm sure you will eventually get your big "O"
I was sexually active with my b/f for over a year before I had my first orgasim and I still dont have an orgasim every time we have sex. Alot of women have this same problem, you are not the only one, trust me. My advice is to relax and enjoy sex and not even think about the "O" , when you think about it, it takes away from the pleasure of sex. and when you worry and try to hard to have one, it backfires. so, just have fun and wait for it to suprise you!!