What could be the cause of vagina pain and pelvic pain on one side?

Pelvic pain: ovarian cyst is a strong possibility. Depending on the side appendicitis could cause this. UTI is another. better get checked by a physician soon

R/O CYST V PID: Unilateral pain can be an ovarian cyst. If you had a recent STD secondary to gonorrhea or clamydia, it can be PID. You need a full exam with pelvic exam and labs. An abdominal and pelvic US to evaluate for cyst/PID/ectopic pregnancy /fibroids. Seek a prompt and through evaluation. If you can possibly be pregnant do a home pregnancy test. An ectopic pregnancy needs urgent evaluation.