Pregnant vs depo shot

Ok i've been on the shot for about 3 1/2 months im due for another shot next week. For a while i would have normal periods just without the cramping symptoms. But about 3 weeks ago my boyfriend and i had sex for the first time and it was unprotected. He pulled out but and my period is only late by 2 days, I'm so scared and stressing about school and my other two children isn't helping. What im asking is could be my stress be delaying my period or could i possibly be pregnant? I knew i was pregnant with both my girls but this time im unsure....