Can't do PIV (TMI Ahead)

long story short, I can't have put anything in my vagina. A penis, tampons, I can barely get passed the first knuckle on my finger without it causing me pain. it's really getting in the way of my sex life. I'm pretty inexperienced when it comes to sex, and I've tried looking up everything in the book. I'm at my wits' end on what to do. I don't have this problem when I do it in my butt. I have no idea what to do. Pls help!