My lower back aches, and how do I releive the pain with OTC meds?

NSAID. Try some mortin 2 pills 3 times a day with meals for a cpl weeks if no relief see your orthopaedic spinal specialist.
Try one. Otc meds can be very effective. Acetaminophen is generally safe, but should not be used by people with liver problems and should not be combined with alcohol. Otc anti-inflammatories like Naproxen and Ibuprofen are good, but can upset the stomach. Folks with ulcers, bleeding problems, kidney problems, high blood pressure should avoid them. If in doubt, check with your doctor.