help?

Recently when I am having sex and *it* first goes in there's a lot of resistance and then after a little while it feels how it's supposed to but it "resets" every time we switch positions. This is with my boyfriend who I'm comfortable around and there's foreplay so it's not an issue where im not relaxed or too dry. I can't see a gyno for a little while so I am hoping for some explanations or tips from anyone who may have experienced something similar before that