I had unprotected sex about 5 days ago and got my period the next day but only lasted 4 days but is usually 7 days, it was lighter than usual and then just stopped. could i be pregnant?

Unlikely, but...: It can be hard to tell if a woman is pregnant because some of the symptoms seen in early pregnancy can also happen in non-pregnant women. That said, a 4-day menstrual period is likely a real menstrual period. If worried, one can do a urine pregnancy test, which gives a reliable result about 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period.