What Causes Burnt Skin On Lip And Arm?

Hi, I have this burnt skin on my lip, left arm and some spot scattered in my upper arm. At 1st I thought I was bitten by an insect, the skin is hot and after a day, started to swell and burn. Leaving a black mark like a bruise.Noticed this 3years ago everytime I'm having a hard time urinating. It always grow back on the same spot and recently I saw new little ones. I want to know if uti causes this?