Need serious help with diarrhea.

Our poor Berner has been having bouts of diarrhea since we brought her home. We’ve taken her to the vet, she got some proviable paste and probiotics and a fecal test (negative). She was doing ok for a week - we feed her Nutro Chicken and Brown rice large breed puppy formula. She was fairly regular. We ran out of paste and then back to diarrhea.

So we thought, well she’s had two bags of this food and it’s been a month and maybe she’s allergic - after reading on here we know fowl allergies might be a cause. Switched her to authority salmon sensitive stomach and skin puppy food, and last night was the worst it’s ever been. She had a good 10-11 diarrheas.

We feed rice and pumpkin. I’m out of ideas and I’m getting seriously tired from being up all night. What can I do - any assistance is seriously appreciated.

Edit: she’s 14 weeks old.