Guinea pigs with mites - being treated by vet with Ivomectin, but skin looks worse.?

My nephew has two guinea pigs he was given as a gift about a month ago. A couple of weeks ago we noticed their skin was flaky and sore, so took them to a vet. He plucked some hair, looked under the microscope and found a LOT of mites. He gave the piggies an injection of Ivomectin each and some Selamectin drops to follow up with weekly for the next four weeks. They seem to be much less itchy now and the skin is no longer flaky, however a lot of bald patches have appeared with bright pink/red shiny skin, and what appears to be raw, traumatised skin. The vet said the mites would get worse before they got better, and the guinea pigs are acting much more healthy and lively than they were, but is it normal for the skin to look so painful and raw while the mites are being treated? Is there anything that can be done to soothe it?