Suggest Cause And Remedy For Itchy Skin

Hi, sir. I am having skin itchy now. Usually when i start walking about ten minutes, i start to feel like thousands of needles hit my skin from the inside from the legs up to my head. The GP i went to said it was sweat alergic, but sometimes when i play soccer or steaming, i did not see the itchy at all and recently, sometime while sleeping, i feel like needles hit my skin too but not that serious as while walking and without any itchy at all. Mind giving me some advice plse? thank you very much....