Late period and stressing

Me and my bf did the deed 2 weeks ago with some government condoms (hundreds of articles saying how reliable and safe they are) and it slipped off after he pulled out to check (before finishing. About halfway) and he put a new one on. But my period is delayed by 2 days and I'm seriously stressing. I'm recently 18 and in my last year of school so that stress might be affecting me. I've been taking 5000mg of vitamin C everyday for 5 days (it's helped keep my periods regular so far) and just. Please help? Maybe some advice or comforting words or something please?