I have a pup that I purchased from a yard in Tx .... when I got the pup the transporter said he had saved the best looking of the 3 he delivered for me. This pup will not gain any weight! He is almost 4 months old and looks like I never drop an ounce of food down for him. The breeder mentioned loosing several pups etc and didn't know from what. I might get weight on him for a week and then bam right back down to nothing. I am feeding Purina Pro Plan, he's on a fatty supplement daily, he's wormed regularly all shots up to date. I am lost? I even ran a round of antibiotics through him.