If your dog is constantly scratching and chewing his leg it could be a couple of things.
Scratching is one of the main symptoms of fleas or mites. Has he been de-flead recently?
You should try to do this every 6 weeks - 3 months to prevent your dog from picking up fleas. However, even if you have been doing this, you should still check them over, as it is not 100% effective.
I also have a 1 year old cockapoo who I used flea treatment on a month ago and she has got them again. It can be quite difficult to pick up on this because of their dense fluffy coats, so look out for the black specks near the roots of the fur.
If he is chewing his leg this could be related to the irritation, or it could also be a sign of stress. Dogs often chew their paws, claws, legs- anything they can reach if they are in distress about something.
Given this, and the sores (which probably need to be treated to prevent infection) I would recommend taking him to the vet to be checked over.
