My upper thighs ache very bad during menstrual cycle. no pain anywhere else besides abdomen and thighs. why are thighs affected during menustration?

Painful menses: Upper thigh pain and abdominal pain during menses can be symptoms of endometriosis. The implanted endometrial tissue at random locations cause abdominal pain when bleeding begins. The thigh pain can result from these implants near to or involving tissue near the sciatic nerves. Pelvic infection can also be increased during menses. See your healthcare provider.