I recieved my period for December on the 3rd. I had unprotected sex that month on the 26th. I recieved my period for January the 4th. The 15th of this month i had unprotected sex. My period for February wasnt expected untill the 5th. However, the 28th (thursday evening) i started bleeding lightly. This lasted until saturday evening. it went from pinkish to red to brown. This wasnt like a regular period. The 1st day of a regular period is always heavy. This has been light the whole time. What is causing this