going crazy

So as of now my period is 12 days late according to this app. I've had protected sex a few weeks back and I've take 4 pregnancy test all come back negative.  I'm an avid marijuana smoker and I was wondering if that's why my period is late? I keep having cramps like it's gonna start soon but it doesn't. And I've had a stressful last 2 weeks.  Plus my mom keeps asking me when my period will be on.. I'm just so nervous and confused.