What Causes Red Spots Under The Armpits And Behind Knees?

Hi - in the last year I have been experiencing large red spots, mainly under my armpits and behind my knees in a cluster, they come as quick as they go but they do itch. Not so frequently I get huge swollen red lumps on my joints and behind my wrists which are again itchy and go as quickly as they come. The only common denominator is I give out a lot of heat but feel cold! I wondered if you could be kind enough to advise - thank you