It would be a good idea to take him to the vet for evaluation. Since he is on Revolution, fleas are an unlikely cause and this isn't typically an area where you'd find them. Possible causes of these signs in a young Pit Bull:
1. Demodex mites- these mites are normal inhabitants of the skin in all dogs. In some dogs, the mite population gets out of control and causes a problem. In an adult, this most often happens in dogs who are otherwise immunosuppressed, but young adult Pit Bulls seem to be more prone (exact reason is unknown) to problems with controlling their Demodex populations. Your vet will need to do a skin scraping to rule out Demodex; often multiple scrapings are needed in order to definitively rule out infection. If it is Demodex and it is just a localized problem, topical medication is usually all that's required. If it becomes generalized, it's much more difficult to get a handle on.
2. Ear infection- yeast, bacteria, or ear mites causing him to scratch his left ear, and by default, the left side of his face. A quick peek in the ear and an ear smear to identify the organisms is all that's needed to get him on the right medication.
3. Hot spot- often allergy related, but the exact cause is usually never known.
Bottom line is that your vet would be the best person to sort this out and get your guy feeling better.
