Other people will probably know more details, but exercise usually actually helps cramps. However, a change in lifestyle can make you period act up, esp. if you changed other things too. I know you've been active all along but it is a different routine. Could you have eaten too soon before running? Could you have gotten those kind of cramps and combined with the other ones it was insane? Or maybe it is random or something else. Good luck and I hope it is better next month!