Sexperts Help Me!

Hey. I’m 18 years old. I just recently lost my virginity about a month ago. I have been extremely safe with it, condoms, etc. But I seem to be having a disconnect somehow. When we are having sex , and go to round 2 or even sometimes the first round... It seems like something goes wrong. I’ll get on top, and he goes soft when trying to enter my hole. Then, other times I’m too tight so I squish him. When I get on bottom, he sometimes can’t get into because I am too tight still. We have tried doggie style and bent over the bed and nothing is seeming to work. Can someone please explain this? Or give me some pointers?