What could be the cause of low pelvic discomfort along with a burning sensation internally. no illness, rash, accident, meds not pregnant but been bleeding every 10days (full period) discomfort moving into thighs?

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. It would be prudent to see a doctor, preferably a gynecologist. You may have pelvic inflammatory disease. In addition to seeing a doctor, take oral iron and multivitamins to prevent anemia from blood loss. Wish you good health!