Neuter issues

My cat was neutered 6 weeks ago, I was advised to leave a collar on for a week which I did. As soon as I took it off a large inch square area of hard skin appeared, it looked like normal skin but was well, crispy. I thought she had groomed it and made it sore. 1 week later I took her back to the vets, the vet did not know what it was but, said it looked fine and would possibly fall off. 3 weeks later, although it had started to lift around the edges, it wasn't coming off. I took her back to the vets where, they still did not know what this was. There was also another area on her thigh near the incision which had lost all it's fur and had gone hard. They pulled off the dry area of skin and she was left with what looked to me like an ulcer. They gave her an antibiotic injection and a gel to rub on twice daily. Tonight this new scab looks to be lifting and again has not healed underneath. I am due back to the vets on Wednesday. She seems fine in herself but, I am very worried... how could they not know what this is? 

Personally I am against using the traditional Elizabethan collar on cats; they are fine for dogs but serious torture devices on most cats, who have a entirely different disposition than a dog.  There are soft inflatable collars that can be used if a cat is really having a problem, but I've found that the take-home pain medication works just fine to make them leave the incision alone.  If it doesnt hurt, they don't bother it.  My vets only use surgical glue on the outer skin so there are no stitches there to irritate them. I think leaving the collar on for a week has indeed caused a "bedsore" type of ulcer, and it's also possible that it's a fungal dermatitis, especially if another spot is showing up in another area.  I would suggest you get a fungal culture done when you go to the vet on Wednesday.  You might even politely ask the vet what he/she thinks about the soft inflatable e-collars (some vets don't seem to even know about these!)