Beginning of Period cramps or possible pregnancy cramps?

We’ve been trying to get pregnant for a while now. Well my last period was the 12-14 of August. I had a positive ovulation test on August 25th. We had intercourse on August 25, 27,28,29. My next period is suppose to be here in 3-8 days. I took a pregnancy test this morning negative. But I’ve had a lot of cramping and back pain. It feels like period cramps in a way but my back has been killing me. I never complain about period cramps and my back never hurts. My periods are usually super smooth and easy. So I’m curious of if this is me about to start my period or possibly pregnancy with the way I’m feeling. No morning sickness or sleepiness more than normal. Any opinions? TIA!