So i had sex four days after my period and it's been a week now and i have white thick discharge and a cramp in my stomach what do this mean?

Any new or unexplained vaginal discharge or abdominal pain need in-person medical attention, and it appears you have both. The combination of abnormal vaginal discharge and abdominal pain or cramping is suspicious for infection, including STDs -- maybe including pelvic inflammatory disease (PID), i.e. Fallopian tube infection. Get care ASAP -- do it immediately if fever or pain is severe.