Orgasming

I know my body fairly well, but I've never been able to tell if I'm having an orgasm during sex. I've been sexually active for 3 years and still don't know if I've ever reached that point during sex. It always feels good, but I've never experienced that "wow" feeling people describe as an orgasm. I've had my boyfriend tell me I've had one, but wouldn't I know for sure if I did? Should I be worried that I haven't experienced this? Or have I had one & just not realized it?