am I pregnant?

I'm 16 and I've had unprotected sex with a 21 year old (please don't judge) my period was late and when it came it only lasted 2-3 days and now I have bad cramps.  I've been super stressed not only about being pregnant but about school and relationships too. I haven't told the guy what's going on does anyone know if this could just be a weird period from all the stress? Or am I pregnant. I'm so scared