I had sex nov. 10th, had my period nov 11th. was normal, lasted for about 5-6 days. Didn't have any other intercourse since nov. 10th, I was under a lot of stress between nov. and dec. because of finals and all my other classes. Took an ept dec. 20th and it was negative, its dec 27th and I have not had my period yet. I have never missed a period but I am somewhat irregular.