My period is late

I'm practically sure I'm not pregant as when my partner and I had sex we used a condom and he always pulls out before he cums anyway to be safe. I'm doing my as levels at the moment and am hugely stressed. Is there a possibility that's why it's late? It's late by 6 days. I'm quite stressed about the fact it's late so could anyone help me out with any opinions? Thankyou