I Have Used My Hot Water Excessively For Years, I

I have used my hot water excessively for years, i do have the dark patterns of purples from what I call heat lines. The last 5 days an unusual blister has appeared on my back, it is black with red raw open tissue surrounding it with a wierd whitish looking bumpy bits in there I'm am quite tender and can not let my bra touch my back as it's sore very very worried
Please can anyone help