Period like pains after running?

I have been training for a half marathon for Tommy’s to raise money for their amazing charity. I took a week long break from training and have noticed my last few runs that I have had BAD period like pains when I get home. I ran at 2PM today, it’s now 6:40PM and I have bad pains. This is both in my uterus (I sometimes feel like I want to push) and my lower back. This has been going on for a few days an my period isn’t due for 6 days. Does anyone else get this?