kikko had a skin problem that lasted for MONTHS! it was at first on his butt and then went the side of his tail, a spot on his hip and on the inside of his ear. kind of like a scabby rash. my vet said it was a fungal infection
we were given a lot of ointments/creams to put on it, worked at first then we had to switch to a new one as it kept coming back. the hair around the area fell out but that was b/c of the medication. and we use a medicated shampoo twice a week .. like someone said its hard to keep it on him for 10 minutes tho
eventually i just stopped with the cream and it got better on its own. i actually fed him a little bit of cottage cheese once a week too, and stopped anything that had even the hint of corn (i think he was allergic to it b/c he'd get itchy and ahave dry skin and just scratch that area more.
let us know what your vet says