Cat mange?

My vet says my cat has allergies, I think it may be cat mange, he scratches alot, wiskers are very short and he has bald spots, he eats science diet food, i have change to natural organic food, nothing helps, what does mange look like and how do i treat it with going to my vet who I think is an idiot. Can’t afford to see a new vet at this time or I would do that. Any suggestions? He is an indoor cat at night and I put out during the day . I really love him, and don’t want he see him suffer, he cleans himself and purrs, but he is ugly looking, Help!

ALLERGIES IS A GOOD CHOICE BUT WAS HE CHECKED FOR RINGWORM? IF NOT DO SO. CATS ARE PRONE TO RINGWORM AND WILL CAUSE THE HAIR TO FALL OUT, AND THIS IS SOMETHING THAT YOU OR OTHER MEMBERS OF THE HOUSE CAN GET.