Freaking out

I had sex with my boyfriend Oct. 25 (Previous period being Oct. 10-Oct. 20) I am on the pill and we use the withdrawal method which I know is not the most effective form of contraceptive and we should be smarter about these decisions. But I should have started my period today, I've been on my placebo pills since Sunday and my period still hasn't come. Realistically, it should have come today, Nov. 10. I'm having PMS signs but am still worried. I may be driving myself crazy but I don't know what else to think. Do you think I could actually be pregnant or is my mind playing tricks on me?