It seems like a more benign form of Pelvic inflammatory disease
(PID). The symptoms of uncomfortable feeling after passing urine, the crampy pain in the lower abdomen and the unprotected sexual intercourse all are features seen in PID.
Unprotected sexual intercourse may be a cause for it, so is not drinking enough water. I do not think a cyst
is a reason for this.
A course of antibiotics will help you. Please practice safe sex
as much as possible or at least until the time you recover.
Get well soon.