Not Getting Orgasm during intercourse but getting orgasm while he is rubbing or fingering me - Getting only pain while fucking

I'm new to sexual experiences and feel pain when my boyfriend penetrates, but I haven't experienced orgasms consistently. We've had sex 8 times, and l've only had an orgasm once. Last time Even after he fucked me 20 minutes hardly I don't get orgasm instead its paining But while he is rubbing, licking and fingering me i am getting orgasm What could be the reason? How can i get orgasm when he fucks me.