Can having a fever (or tylenol/naproxen taken to control the pain and fever) cause prolonged menstrual period (12+ days)? my personal was always 6-days long in a 27-day cycle in the past. can abnormal bleeding be related to the fever(no pelvic pain)?

Menorrhagia (vaginal bleeding beyond 7 days) is less likely caused by fever and a couple days of using antipyretic agent. You can observe for now but if menorrhagia recurs next month or if you have bleeding again before the next cycle then you need to see a GYN doctor for ruling out structural or hormonal abnormality. Good luck.

Prolonged periods generally occur from hormonal imbalance and some local genital causes and not from fever which is the body's reaction to any infection, inflammation or environmental affect.