first time painful, others were worse. what's up with that?

lena
so recently my girlfriend and I have been having "sex" (fingering, eating out, ect.) and while I love her with all my heart, it is just painful. in a "common" sex viewpoint, I am a virgin (I haven't been with a male). we've been doing this for quite some time, yet each time is a little less painful than the last time we did it. I'm scared that we may have bruised something in my vagina; but at the same time I don't feel comfortable telling a doctor. is the pain I feel due to the lack of actual female-male intercourse? or is it something that has to do with the actual "sex" itself?