I would still go to the vet appointment tomorrow. It's still very likely that it could be a reaction to the Ivermectin, and the vet will need to figure out what else to give you to treat the mange.
Some acorns are poisonous to dogs. I highly suggest researching to find out which ones they are and if they're the same ones in your backyard. Google searches should do the trick.
I'm glad to hear that he did eat tonight, and I would just let this go if he was not eating. But.
The only person who can determine if you're "spoiling" a dog is yourself. Spoiling means that you are causing the dog to be an inconvenience; for example, if you say, "My yorkie HAS to come with me everywhere I go, in my purse, even though it's annoying to me and gets me kicked out of stores," and proceed to carry the yorkie around anyway, you're spoiling him. If you are ok with feeding your dog *healthy* foods off of your plate and straight out of your mouth, and it's not inconveniencing you or the dog, then by all means go ahead. And don't let anyone tell you otherwise.
That said, you can teach a dog to be a picky eater. If you offer him food, and he doesn't eat it, so you offer him something better (and he's healthy), you are teaching him that NOT eating will get the GOOD stuff. Just like kids - I have a neice who won't eat anything "healthy," she will basically only eat mac and cheese. Why is that? Because whenever she decides she doesn't like something, her mother makes her mac and cheese so that she has
something to eat. She's learned to be a picky eater.
If your dog doesn't eat his kibble, then he doesn't eat. If he does eat his kibble, THEN you can consider giving him tastier stuff.