Period help??

Okay, first time posting here but I need some opinions! My period is officially 15 days late, the chances of me being pregnant are slim, I was already late when my boyfriend and I first (ever) had sex, and before that the last time I had sex was August and ive had periods since then. Ive had cramps but I just won't start. My cycle has always been weird, but im very worried that this might possibly be pregnancy. I guess I'm just wondering if anyone has been through anything like this? Is missing a month normal sometimes? (Also, not on the pill or any form of bc).