I Have Been Suffering From Sudden Onsets Of Localized Rashes

I have been suffering from sudden onsets of localized rashes that appear suddenly on different locations of my body. The rash usually covers an area 5 to 7 inches wide, red in color with localized fever and intense itching. 24 hours later a hard red nodule about the size of a pencil eraser appears. One of the unusual things is that this seems to be happening about every 2 to 2 1/2 weeks. Please don't tell me it's bug bites as I have had 2 different extermimating companies do inspections with negative results. This has been going on for about 4 months now....I feel desperate!