Hope your little baby starts feeling better .. Remember you changing his food will loosen the poo up to.. I give my babies Eagle Pack Chicken and Rice.. Albon is great and see if the doc will give you some of that .. did he test for everythin g Parvo. Geaurdia sorry spelling... that is what it sounds like. make sure you give him some karo syrup to keep his sugar level up.. and you might need to take him to another vet... Good luck
