Sex during pregnancy question!

So I'm estimating im about 10-11 weeks. my fiance and i were having sex, I was on top and I leaned back and as he was *ahem* still going in and out of me, I felt an organ (my uterus possibly) push up towards the front of my belly. It did this about 3 or 4 times until I leaned forward again cuz it was just uncomfortable.

Sorry for the tmi, but has anyone experienced this before? I'm not in pain, I feel the same as I did before. It was just a strange sensation :/