I had sex on my 4th day of my period? do i need to take the emergency pill? is there a chance i will be pregnant?

Depends on cycles: A woman should not get pregnant by having sex on the fourth day of her normal regular period, unless she has very short cycles. She does not produce an egg during the first days of her normal regular menstrual period. Of course, she might get pregnant if sperm from the day 4 sex survives through day 10, and if she ovulates on day 10. That might happen if her cycles are shorter than 24 days.