I’m having pain during sex

So a little over a month ago me and my boyfriend were having sex and I notice pain around the entrance, it was like a stinging pain, I didn’t say anything cause it wasn’t too bad. However we had sex last week for the first time since then, the pain was there again but it was worse I told him it was hurting too bad and I couldn’t continue. We’ve had sex before and I’ve never experienced this pain until now.

I don’t know if this could have anything to do with it but I’m a few days late on my period, I’ve never been late before. We used condoms (the last few times but not always) and I took two pregnancy tests and they were negative. But I’m wondering if something could be wrong that’s causing these things.

I’m also only 20 and haven’t really been to the doctors for this sort of stuff and don’t even know where to go. Do I need to go to an obgyn or can I just go to a regular doctor? Any help on what this could be or how to even go about going to the doctors would help. Thank you so much!