Ihave Pain Only If You Touch One Specific Spot Under

Ihave pain only if you touch one specific spot under my left arm (like deodorant) an it spreads out to the side of my upper side arm. There is a perfectly circle white scaley patch and a red raised bump that the pain radiates too. Also if I use this arm to reach to the lower middle of back it is so intense that i scream and if i am holding something i drop it. on set was sudddenly.