Diarrhea in a 3 1/2 month old GSD...I am at my whits end!!

I am really out of Ideas here. my 3 1/2 month old female GSD has had diarrhea for 4 days now. My vet doesn't really have any more idea's at this point. We have tested her for Coccidia, Giardia, worms ( we then wormed her with Panacur, just in case) she's on Probiotics to help keep her digestive tract healthy. She was tested for Parvo, negative. She is eating, drinking, playing and acting completely normal, maybe not playing with her tug toy as much. We have dealt with a lot of diarrhea since bringing her home, 1st she had worms and ate a big ol' cow pie before I could stop her, her food was too rich so I am giving her chicken and rice and that cleared it up, I have been slowly integrating her new kibble into her food and she seems to be doing fine with it. but she wasn't gaining any weight because there just wasn't enough protein in her diet. So taking my vets advice I added some browned and fat drained ground beef a little at a time to her food, and now she's gaining weight beautifully, her coat is nice and shiny, and she just looks wonderful, but she's got diarrhea again, and some gas with it. Sometimes its semi-solid, and occasionally it is just plain runny brown milk shake, so today I gave her some pumpkin in her food. I don't really know what else to do, and my vet isn't really helping at this point. Has anyone else dealt with their pups having a lot of diarrhea at a young age? I kinda feel like the poop queen at this point:help: