Pan gets them from time to time. Some are worse than others. We took him to the vet and were told it could be an allergic reaction best case, or worse case it could be lupus. We are on the wait and see track. We switched his food and keep his paws clean and dry and we haven't seen them since.
I would suggest at minimum getting some medicated wash to clean his feet until you can get in to see the vet.
When Pan had his first outbreak I called and made an appointment for the following Monday, it was the longest weekend ever. By the time we got in he was in so much pain that he didn't even want to walk. Two days on the steroid and he was super dog running around the yard doing his crazy bulldog run.
Good luck and keep us updated.