I get cramp on my legs, calf muscle, why this? What should I do? I'm 37 years male

Nocturnal leg cramp. Do these occur at night? These are called nocturnal leg cramps. The classic treatment for these is quinine at bedtime, but because of washington dc politics within the fda this medication is no longer availble for us to use to help you. You can stretch at bedtime, stretch when you get these or try to prevent them by drinking quinine water at bedtime. I agree with dr skow -see your doctor.
Many reasons. Cramps in the calfs can occur for many reasons. One could be from electrolyes such as low potassium. Another reason, particularly if worse with excercise and better with rest is blood flow. When you excercise, your muscles need more oxygen which comes through the blood. If there is decreased flow, then your muscles dont get the oxygen they need and cramp. I would see your doc.