Cramps bfp feels like Af cramps

So I've had sexual activity with my boyfriend and the next day at night I had cramps that felt like my period was starting but its way too soon for my period to start what could it be yes I've done research and found out that ovulation can come anytime in a woman's cycle and the 14 day rule is a myth yes I believe this cause I do tend to cramp up during ovulation but for some reason I think this was different someone help