Suggest Treatment For Itchy Rashes On Face, Back, Buttocks And Thighs

I am suffering from skin rashes and itching from the past 3 months.doctor has advised zyrtec. The rashes and itching disappear for one and a half day after taking the tablet but again appear. The rashes are mainly in the face,back,buttocks,palms,hands and inner thighs. Rarely they appear in eyelids and lips also. Please help