I had sexual intercourse a week before. And I had my period today. Does that confirm I am not pregnant.

It is unusual to have a "period" during a pregnancy - but it is not unheard of.

I would assume you are not pregnant. You could always buy a HPT kit and find out 100%.

I am sure you are not pregnant because the lining of the womb starts to deteriorate as the hormones that sustain it in peak condition alter. After a few days, the lining breaks down completely, sloughs off the wall of the uterus, and is washed away by the blood released from the arteries that supplied it. Contractions of the uterus also help remove the debris.

After 3 to 5 days, the bleeding stops, and a new lining starts to develop ready for the next months ovulation.