Based on the infection it seems like you are having abnormal vaginal bleeding
, may be associated with pelvic inflammatory disease
(PID) which explains the creamy white discharge.
The PID may be caused due to some kind of infection, as you are sexually active and you have white creamy discharge it seems like a "FUNGAL" infection.
ADVICE:- You need to see your physician soon, in case of excessive pain in the stomach may need to go to emergency room.
Hope it helps.