Sex is suddenly painful?

I just got back together with the guy I lost my virginity to, everything has changed for the better, he’s really grown as a person and that’s why I decided to give it another try.

We’ve been having consistent sex since October and it’s been amazing. The whole time there hasn’t been one painful experience so far. But tonight was SUPER uncomfortable. I can’t even describe the pain. And when I went to go clean up in the bathroom, the discharge was pink. Which has happened once before too, years ago. I assumed that he was hitting my cervix and that I just wasn’t as “ready” for sex as I thought I was (I was in the mood all day but we were either out running errands or spending time with his family lol) but I had asked him if he felt any difference and he said no. I explained the pain and he said “well since I’ve been losing weight, there’s been more length, maybe I did hit it, I’m so sorry, I’ll be more careful next time, are you okay?” Which checks out, he had lost more weight in between the last time and this time. I just wasn’t expecting the pain. I had just ended my period on Friday. I thought maybe that had something to do with it, but we’ve had period sex before as well as sex RIGHT after it ends and it’s never been this painful. The initial position was Doggy if that helps 😅 which we do often because it’s usually my favorite/feels the best. Do you have any idea why it was suddenly painful?