What Causes Red, Sore And Lumpy Spots On The Leg?

50 year old female living in hot, humid Florida. I have a red spot on my upper inner thigh about the size of a quarter. It is red, sore and bumpy. This spot appeared last summer and I thought it was due to a spider or other insect bite ( i had some mosquito bites on my legs and woke in the middle of the night due to pain/itching where this spot occurred). It became an open sore for a while then cleared up (took a couple weeks). Now it is back. It has not spread or appeared anywhere else. If this were herpes or shingles would it appear in only one spot?