Good day to you. Thanks for the query. You have skin rash after taking first dose of CoQ 10. I think that you are allergic to CoQ 10. You should immediately stop this medicine. Take some Anti histamine like Loratadine . If there is severe itching , increasing rashes, swelling of face/lips or breathing difficulty, immediately consult doctor. About your problem for leg cramping every 3 to 4 weeks, I want to ask some questions, Are taking any medication for regularly? are you diabetic or having some vitamin D deficiency. Is the pain related to activity or it occurs at rest. Does the pain occur at night?,Do you have prominent veins in the legs? I would suggest that you undergo some investigations like Complete blood count, fasting blood sugar, lipid profile, vitamin D levels, Vitamin B 12, electrolytes, liver and kidney function tests, calcium, uric acid, thyroid profile. If all tests come back normal , do doppler studies of the leg arteries and veins. It should be properly investigated before taking any supplements or treatment.