I'm so glad you're taking him in
. He may have a flea allergy too - and those can be just miserable for dogs, very uncomfortable. Until you see the vet on Monday, there are a couple things you could try -- get a Benadryl Pen (it's like a pen that has liquid Ben. in it, and it's for topical use) and put it on the area, give him oral Benadryl (dosage appropriate), put hydrocortisone cream on the area.