Discomfort in certain sex positions...

I know it’s fairly normal to experience mild discomfort in certain sexual positions (ie doggy style), however WHERE is “normal” discomfort felt at? Specifically, my husband and I were having sex last night and I was on top, facing him. The more I widened my legs around his torso, I felt mild discomfort in my rectum. I’ve never felt rectum discomfort with sex before. Has anyone else experienced this, and is there any reason for concern? For what it’s worth, I’m on the tail end of my period. I also have a tilted uterus.