NEW, UNEXPECTED PAIN during/after intercourse

I (19F) have been with my partner (19M) for 8 months and we’ve been engaging in intercourse for that length too. I’ve never had an issue with pain during/after sex, until last week. We were doing things the way we normally do and have been doing for ages, when suddenly I got a super sharp pain deep from my cervix all the way out to my vulva and even my anus. For reference, it feels exactly like the sharp muscle spasms that randomly happen in your anus. It got worse whenever he went further in, but when he wasn’t in, the pain would just randomly spike and then fall off, then spike again, like contractions.

My partners eggplant size is about 6”, perfect size for me and has never caused issues.

We did it again today and it started off fine but quickly it started to hurt the same way. It’s been about an hour since we had to stop because of the pain, I’m still getting almost contraction like muscle spasms, mostly just in my vaginal cavity area and my anus. It really really hurts, but it’s slowly going away.

I’m just concerned because it’s very random and I don’t like that it’s happened twice in a row, makes me worry. I thought waiting a week would fix it since I didn’t have any pain for that long, but like I said it came back quickly after starting.

I don’t get period cramps, I have no conditions, I don’t take medications, I am a very healthy person as far as I am aware. I’m not pregnant as I took a test about 3 weeks ago which showed negative.