Bled during sex, not period?

I bled during sex about a week ago and figured my period just got kickstarted a few days earlier. The next day I wasn’t bleeding and now my period is late by 3 days. This is the second time to happen to me, but the first time happened almost a year ago. I have the IUD so I didn’t know if that could be it, but I figured I would have felt some pain/discomfort if it was because of that.