Late period

I'm having a nervous breakdown because I think I may be pregnant. My boyfriend and I had sex about a month ago with a condom and I was on the last day of my period. He came in the condom inside me but it didn't break. My periods three days late but he keeps saying there's no way I can be pregnant. I'm still nervous! I've heard it could be late just because I'm stressing about it...please advice is needed!