[Help] My dog has a weak immune system - any suggestions for supplements to help?

My dog is a year and a half old mix - hound/pointer/lab maybe? Anyways, I swear we don't go more than 3 weeks without ending up with some kind of infection. He just recently went through a round of antibiotics for an abscess he got, which lead to diarrhea and an inflamed rectum. We got through that, and he cut his mouth on a chew bone, ended up with an infection that made his lips swell up, more antibiotics and anti-inflammatories. Most recently, he did something to his paw. Vet can't figure out what, but there is definite infection so the vet gave us a boot and some specialized wash for his paw that we have to use twice a day because she's afraid to keep putting him on antibiotics.We are wondering if there is anything we can add to his food to help naturally boost his immune system? Has anyone had success with anything? via /r/dogs http://ift.tt/2rEh1Du