Periods after sex.

Okay, I’ve been showing symptoms of my period coming. I’ve had several mental break downs in the past couple days, me and my boyfriend had sex on the 7th and my period hasn’t came yet. It’s been 3 days late and I’m getting worried, is this normal? I haven’t discharged anything whatsoever, could my period just come late since I had sex? This has happened before and last time it was in May and it was almost 7 days late.