Crusty ears and very itchy.

i have a boston terrier that just turned 1 year old (female). at 6 months i took her to get spayed. upon removing her cone 10 days after the operation, i noticed the back of both ears were bald. and since that very moment, she has been almost nonstop itching. took her to the vet, and the vet did skin scrapings multiple times but never found anything. vet wanted to do expensive allergy testing which i have low confidence in.

she has developed a rash under her belly. it gets particularly bad under her armpits and neck. she scratches herself till she bleeds. one thing i notice is that her ears are the most itchy part. she is always rolling on the ground trying to get that itch hat appears to be inside her ears. sometimes, they get really inflamed. she has developed hyperpigmentation behind her bald ears. she does not have any unusual discharge coming out of her ear. but she does have a bad odor to her body. her body feels like it is sweating, and sometimes she will have localized areas on her front legs and chest that will ooze and wet your hands when you pick her up. she also develops these brown crusts on her legs and belly. i did the pedal pinna test and she kicks her back leg like crazy. but she will also kick if i scratch the back of her ear, and sometimes top of her head and her neck, which has also gone bald. she is losing hair around her back legs (about the size of a pea).

she has been treated with antibiotics by the vet for weeks (cephalexin i think). no affect.

on my own, i decided to treat her for sarcoptic mange. she weighs 18 lbs. i gave her the revolution that is for dogs 10-20lbs. i gave her the third dose already and it has been 45 days since her first dose, and she does not appear to be improving. She may have gotten worst as I noticed the tip of her ears began to crust (which I had never seen before) a bit after her initial doses of revolution, although it went away yesterday. the revolution doses were given over 2 week intervals. she doesnt look better. at first, i thought it was working cause she appeared to get worse but then got better. but then she got worse again, and then better, and now is worse again. when she gets better, it lasts a matter of days before she gets worse. in the morning, he rash is not bad, but it gets worse as he day progresses.

my question is, given that i just gave her the third dose of revolution, shouldnt she be better by now if what she has is in fact sarcoptic mange? Or should I wait until 60 days has elapsed and expect a sudden positive change? I didn't know if a 4th, 5th, or even 6th dose was warranted of revolution

My vet recommended trying imermectin given orally. I dont like this medicine due to the risks. Should I try Advantage Multi instead?

i tried changing her food. when this all started she was on innova puppy. then switched her to natural balance limited ingredients bison and potato. now she is on nutrisca that is lamb and chickpea.