I had sex and a few days later I got my period. Today I woke up with a sour mouth and nausea. Could I be pregnant?

Maybe not... A girl or woman cannot get her regular period and be pregnant at the same time. However, she can get pregnant a week or two after her regular period. If she has some spotting or light bleeding that doesn't look like her normal regular period, she can check a urine pregnancy test about 3 weeks after sex (3 weeks after when conception might have happened) to see if she is pregnant.