What Causes Painful,red And Swollen Bumps With Itching On Body?

Hi have been breaking out since january. It starts off looking like a bug bite. It is very itchy and then by the third day it is very hot with fever, painful, red and swallon. I have been tested for several things, from mercer and lime disease. The only thing about it is it leaves a dark spot once it goes away. I have been on different anitbotics and still it comes back. It will even come back again in the same spot. It comes back as hard bumps and then it starts to itch all over again. I have even been to a diease specalist and they are not sure what it is. They are telling me that it is a bug bit, but it keeps coming back. I only break out on my hand and arms. Once on my ankle. Any idea of what this may be?