“Reoccurring itch and rash?”

I have been seeing a doctor for over two months now for a reoccurring itch and rash on my the top of my hands and forearms. They have been giving me prednisone and Advantan cream which will clear it up and stop the itching. but the itching comes right back once the treatment end, which causes me to scratch and the rash to reappear. I do not want to take anymore of the steroids because it makes me really drowsy and causes my heart to speed up. The itching and rash breakout began when I decide to do some weeding and additionally while weeding I get bite by mosquitoes and I think sand flies. can you help me figure out what is the underlining cause because right now my doctor only seem to be guessing.