late period :(

I'm sexually active but we have always used condoms and we only had sex one time since my last period, and I'm positive the condom didn't break. But I'm 4 days late and am stressed out to the max, which I know can cause your period to be late, and I'm also on Christmas break which changed my routine a lot so there are definitely factors that could be affecting it but I'm still stressed about being pregnant. I haven't had any pregnancy symptoms and I've had on and off pms symptoms but it just seems like my body is refusing to actually start my period, should I keep worrying? What should I do?