First period

I got mirena when my son was almost 2 months old so I've had it about 2 years now. The last period I had was the period before finding out I was pregnant.

I had sex earlier today and I've been cramping really bad ever since, my stomach hurts, and I'm kinda nauseas. I just went to the bathroom (it's been about 6 hours since I had sex) and I'm bleeding. I checked my strings and everything's still in place. Is it probably just my period?

Also, I've had sex multiple times since having it & I've never had an issue. I've had very light spotting here and there but that happened before I got mirena, too.