Keep Getting Painful Rash On Legs, Tenderness, Burning, Itching, Swollen. Permanent Cure?

I keep getting a very painful rash on my legs. It will develop in one or two spots, with each spot appearing roughly circular. Before anything shows on the skin I will feel tenderness and itching/burning. After a day or two the rash will show up with small blisters that appear white. The circles will also be ringed with redness and the circular area is swollen and raised. It is very painful, almost like a very bad bruise. I can't touch it without pain and even clothing rubbing on it hurts. After several days the blisters will break and a clear liquid leaks out. Then the area will scab over, but only where the blisters burst. The scab does not cover the entire affected area, as in there is not one big scab. When the scabs finally disappear I am still left with a darkened area for several months. They come back every 3-4 months, and always appear somewhere on my legs, though usually they are on or near my knees. My most recent outbreak is currently in the middle of my thigh.