Is Prednisone 20 Mg Tablet Effective For Red Rash Under The Skin?

My dermotoligist prescribed me Prednisone 20mg tablet on 02/21/14 of which I had taken 01/07/14. The prescription I took in January was for a sinus infection. I had a red rash under the skin and the new prescription 02/21/14 is for this cause. I have always been told not to take it more than three times a year. I have not started this medication yet. Please advise me of what I should do.