No orgasm?

Every time my partner and I have sex, especially if I'm on top, it feels mindblowingly good but I can never seem to orgasm. Today we went for quite some time and I felt like I was close, but never could quite get there. After awhile I told him it wasn't anything he was doing wrong; I had no idea why.

I'm not all that disappointed, as I really love sex with my partner regardless of orgasm and it feels fantastic, but I was wondering if any other ladies had the same problem?