paranoid or pregnant?

So me and the other half had unprotected sex for three days during my fertile window, now my period is late, I'm getting headaches a lot, some cramping, a bit of sickness and constipation (sorry!) any idea? My periods are never late, if anything they're always a few days early! I'm not stressed or anything like that so no idea what it is, always wanted to be a mummy, now I'm nervous but excited if I am