Last two days bad pelvic/lower back pain. period ended 3 days ago. tried motrin and tylenol (acetaminophen) but nothing is helping. not sure what else to try?

Several options: Back pain is usually related to arthritic changes to the spine. Sometime back pain can be related to infections, cancer, fractures, or even other organs such as the kidney, bladder, etc. Usually pain will improve over 1-2 weeks with rest and anti-inlfammatories. If the pain last longer than two weeks I recommend seeing your physician.