Skin reactioon to cystos

(I also posted this in urology)

I've had bladder cancer since 2000 and have undergone numerous cystos, TURBS, BCG/interferron treatments. Nothing in muscle, but just got a postive FISH. A couple of years back, I started getting rashes at the tip of my penis and above the anus immediately after each cysto. I told my urologist, who didn't have an answer and they continued after each cysto, getting worse and taking longer to resolve each time. We tried switching betadine with another prep solution; no effect. My urologist thinks it has nothing to do with the cystos and is fungal. I know it has something to do with the cystos. I asked my wife to examine me beforehand and afterwards. The rash appeared immediately after the cysto. My urologist prescribed an anti-fungal cream which I've been using for two days without much effect. The skin on my penis in two areas in purplish-black.On the advice of my GP,  I am going to see a dermatologist. My question: Could it be an allergic reaction to lidocaine? Or possibly the solution (Cidex?) they use to clean the scope? Have you heard of this type of reactions to cystos. This is really bothing me and interrupts my sex life and makes working out painful too.
One other issue: I get a lot of false-postive FISH tests, which lead to a biopsy, which eventualy leads to a "no cancer" report. I'm thinking of dropping the FISH test and just relying on cystos and NMP cytology tests. Is this advisable?
Thanks in advance