Addie, Did your vet instruct you to thoroughly clean the cage parts and throw away wooden perches and replace with new ones? Those nasty little mites bury themselves in the crevices of perches and in the cracks of metal cages during the daytime and then come back out to feed off the poor little bird during the night time.
I have never had a pet bird with mites but I know how hard they are to kill. Our wild birds, mostly sparrows, leave mites all over my patio and they get in my hair and drive me nuts with the itching. It takes days of shampooing with special shampoos, over and over, to kill them.
Hope Spike gets well soon.
Annie