I Have Had Protected Sex The 16 Of Last Month

I have had protected sex the 16 of last month and I missed my period. I have really irregular periods. It's either at the beginning or end of each month. And some times going a month without it.my last period was 9 days long and ended the first of December last month. I have been stressing if I'm pregnant for almost 2 weeks. Could my stress trick my body into thinking im pregnant? Should I take a test just to ease my mind? Also I have been getting a pain around my left pelvic area...like a sharp pain. And it usually causes me to bleed heavily. What should I do? Thank you for your time.