I have period like cramps 3 days after menstruating what can it be?

Endometriosis is a good bet, given the nature of the pain and timing with menstruation. If you're at risk for STD, and especially if you also have other symptoms like vaginal discharge, pelvic inflammatory disease (PID) is possible. Any new or unexplained pelvic or low abdominal pain should be professionally evaluated, so see your doctor soon. Good luck.