My 10 yr English mastiff has been battling for awhile with these sores he gets on his chest, legs, sides, & back. We take him to the vet they say it's bacterial infection and put him on antibiotics, it goes away. Within 2 weeks .they are coming back. Plus he's had loose stools too. He has been on antibiotics 4 times and I don't want to keep giving him pills all the time. I'm thinking he is allergic to something in his food. Any suggestions on food we can look into?