Hi,
sounds a bit like ringworm. Not a worm. A fungal skin condition. You can catch it from infected animals or other people. Can be treated with anti-fungal creams like canesten, lamisil etc.
It is worth going to the Doctor, as some people say Lymes Disease looks similar, more like a bulls eye apparently. But that illness is more serious. There is also a condition called Pityriasis Rosea which causes reddish marks. You could do a search on the net might give you an idea, but do check out with your doctor.
Sorry I know these things are distressing,
take care
M.B