Diet or drugs? Medications can increase risks of leg cramps as can nutritional deficiencies. If you are taking medicines or have an unusual diet talk to your doctor about testing for low potassium or magnesium levels or anemia. You can try tonic water or mineral supplements. If one leg is swelling and cramping more that the other or is much colder, do not ignore that... It could be a sign of a clot (dvt).
Could be veins. One of the most common symptoms of varicose veins and venous incompetence is leg cramps. As much as 70% of the time, people with varicose veins will have leg cramps. Although there are many other possible causes, as others have said, if you have any visible veins in your legs, you should see a venous specialist (phlebologist) for help. Fortunately, it probably isn't a clot.