Hello Sir, I Am A Normal Guy With 5 Feet

Hello sir, I am a normal guy with 5 feet and 6 inch height 60 kg weight. I look normal but my legs are abnormally thin , some times i feel pain if i travel longer time or standing for hours, after sex i feel as my legs are paining. I have done many exercise for legs but no gain. I have pain only in my legs . Plz tell me whats wrong with my legs.