Hello, Thank you for using healthcaremagic. I read your question and understood your concern. Until now we are told that muscle cramps are caused by low magnesium and low calcium in our bodies. The newest and most scientifically supported theory is that muscle cramps are caused by premature fatigue. As you get tired, your muscle’s reflex control becomes dysfunctional. Instead of contracting and relaxing like they’re supposed to, they keep firing. Basically, your muscles become “twitchy” and can’t stop contracting. That explains why you have low andurance during sex. I advise you to go to your family doctor and make a complete blood check and examination for this problem . Wish you quick recovery. Dr. Selmani