While I'm sure it's possible that something more is going on, and, depending on the pain you're feeling, should possibly have it checked out, i can also say that I got my period sooner with each subsequent child (to the point where I got it two weeks after my lochia stopped with #3) and, particularly with #2, my first periods were quite painful as well. Also, particularly with #3, they have been both very light and rather unexpected, coming not quite on the date I usually expect them (I'm generally like clockwork). I raced to my doc the minute I skipped a period after #2 and she said not to expect things to be normal, as I was exclusively breastfeeding (as I did with all of my kids).