Help me figure this out

I have had nothing but protected sex. but I had sex the 19th (protected) and he finished early so he pinched the tip of the condom took it off and put a new one on. He swears that he didnt get any cum on the new condom. I was supposed to start my period the 21st but I'm 2 days late. i have been irregular before. like my period sometimes skips a month. I've been very stressed lately due to school and college. I was spotting for a few days then we had sex and it stopped. Someone please give me an idea of what is maybe happening.