What Causes Itching On Body Mostly On Breast And Groin?

I have been itching all over since memorial weekend. I thought it was due to allergic reaction to pencillin, but doc said no. gave me steriod shot & clartin. I will finish claritin tomorrow, but still itchy mostly at night & mostly in certain areas breast & groin. what is this? I am 37 yrs old, 144lbs and tired of this itch!