Help please

So my period was a day late. No biggy samething happened the last time I had sex. Everytime had been with a condom and everytime he pulled out except once. So I got my period earlier today and normally it's slow at first but usually is a continuous flow but it's seemed to stop. Like I must of bled for a few hours and then just stopped it wasn't even bright red either. I've had normal pms symptoms(cramps, moodiness, sensitive nips) except my cramps were worse. I want to hope it's due to stress or something but I don't think I'm that stressed. Could it be something serious? Any information is grateful.