The gassiness may be due to not having as much in his gut after a bout of diarrhea; it takes a couple of days for things to get back to normal. Sophie picked up hookworms; vet said it might be from her not-so-secret vice of eating rabbit droppings. We try our best to prevent it but unless we keep her on a short leash all the time and never let her patrol the yard she manages to find them. Corgi persistence, you know! Our first corgi used to get bloody diarrhea, which was diagnosed as basically doggy irritable bowel syndrome. We changed her to a special kibble and she did fine. Good luck!