Hello, I have gone through your query and understand your concern. I suspect it to be due to Shingles (Herpes Zoster). Because you are pretty sure about not a dermatitis or fungal infection. Further you have rashes under the breast with shoulder blade pain on the same side and fever. It is an infection of a nerve area caused by the varicella-zoster virus. It causes pain and a rash along a band of skin supplied by the affected nerve. This need to be confirmed by visual inspection by your treating physician. He may start antivirals like acyclovir or gancyclovir. He also prescribe pain killers like Ibupfofen for pain and antidepressents like amitriptyline, imipramine, and nortriptyline for nerve pain. If the rash is severe, he may refer to dermatologist for laser therapy. He may give pulses of laser to reduce the pain and rashes. he may give varicella zoster vaccine after treatment. Hope this helps. Please write back for further queries. Wishing you good health.