Can't orgasm when doing oral

I'll be 20 in a couple of days and my bf is 21. He's my first and I never been sexual with anyone else. He's so sweet to me even after I have had some problems when we are intimate. First my hands would fall asleep for a good 20 minutes or more whenever he went down on me. Also it rrally hurts me when we try to have penetrative sex. However, I can't orgasm when he goes down on me. Most girls do but I can't. We foreplay for a long time and he goes down on me for a long time and also fingers me.

How can I relax myself so that I can orgasm?