I can't believe no one has suggested Natural Balance Duck & Potato for you yet. Buster had same prob for 6-7mo. He tried wellness puppy (by far the worst..way too rich for a dog with sensitive stomach...although they have since released the simple solution, which wasn't available then), Chick soup, nutro, and then NB Duck & Potato. After a few weeks on NB he started stiffening up. I do think that we switched way too much, expecting results too fast. Don't expect them to firm up within a week (or even 2 or 3 for that matter). It seems as if NB D&P is one of the best options (besides raw) for dogs with sensitive stomachs. As I said though, stick with something for awhile- and I bet that Wellness SS is similar to NB D&P. We had Buster on like 4 different foods between 7wk-6mo, not including what the breeder had him on before that. Complete error on our part, and who knows, maybe he would have had eventual success if we hadn't interfered. My advice is choose something w/very simple ingredients, not too rich, and stick with it for at least 1.5 mo. Now, Buster is rotating on NV Prarie, and doing awesome.. I know how bad it sucks, 6 mo of soft serve was horrible.