mange, abrasion or allergies?

[Kit]

First off, Yes I do have a vet appointment scheduled for tuesday.

My pup has developed a couple of quarter sized spots on his side and back legs that are slightly red and slight hair loss. He also has one spot on the back of his neck, but I think thats from his old collar. We changed collars as soon as we noticed it. They seem to come and go within a few days. He has also had a few days with discharge from his eyes, so I'm think allergies?
Not sure if this is mange, allergies, or just abrasions from puppy play at the dog park. Are there any other conditions I should consider and research before our vet appointment? I like to prepared with questions for the vet when we go in.

Puppy is a 4 month mix, medium large breed, shorthair, no medical problems known. He has his shots and vaccinations. Has no other problems. Eats well, is energetic and alert throughout the day (when not napping) stool is normal.
Forgot to mention fleas and such. I haven;t seen fleas on him, or in the house, no itching or discomfort either.

Every night we have a ritual of the puppy sitting or standing quietly while I check his body, ears, paws, mouth, etc. It gets him used to being touched all over, and lets me look for any problems like sore pads, scrapes from the dog park, infestations, etc.