Is it normal that it hurts after my period?

If I have sex the day after I finish my period I'm usually in a fair bit of pain and it gets a little red and swollen down there.
Once I also had a lot of discharge, but otherwise the discharge seemed normal.
This has happened a couple of times, but it's usually fine after a couple of days. It never hurts if I have sex any other time of the month.
Should I be worried?