For back pain caused by cramps (often associated with menstrual cramps), over-the-counter NSAIDs like Ibuprofen (Advil/Motrin) or Naproxen (Aleve) are generally the most effective medications because they target the prostaglandins causing the cramping. If you cannot take NSAIDs, Acetaminophen (Tylenol) can help manage the pain. Applying a heating pad to your lower back can also provide quick, non-pharmacological relief. Because you describe the pain as severe, I highly recommend consulting a healthcare provider to ensure there are no underlying issues and to discuss prescription-strength options or muscle relaxants if needed.