Scared and need help

So I really want to have sex with my boyfriend but I am absolutely terrified of anything going inside me. I can't put a tampon in because I get so freaked out. I have a disease that requires me to self catheterize and as a kid I was poked and prodded down there all the time at doctors appointments. I am so freaked out about anything going on down there and I don't know what to do to help.. Any advice?