orgasms??

so i've never had a vaginal orgasm. plenty from the clit but never vaginally. i've never been able to figure out how to actually get there. my boyfriend and I had sex a couple days ago and i felt this weird uncomfortable feeling that i've never felt before and i actually made him stop for a minute because i didn't like it. so i guess my question is, for those of you that have had vaginal orgasms, what is it supposed to feel like leading up to it and how do i know if i'm close?
also what was that weird pressure i was feeling like was that almost it or nah