Chronic puppy diarrhea

I have a 5 month old English Labrador. When we first brought her home she was diagnosed with giardia and was symptomatic with diarrhea (still great appetite and energy). She’d been on the same food the breeder was feeding and on probiotics since we got her. We treated with Drontal. Next giardia panel came back negative but the diarrhea continued. We did a week of Flagyl which got her poo about 90% normal. After stopping the Flagyl the diarrhea returned. Diarrhea PCR came back positive for c.perfeingens alpha toxin gene but technically still wnl. We switched her food to Purina sensitive skin and stomach puppy with salmon, no change. We tried adding in E/N fiber balance which firmed her stool but made the volume so great that even being fed dinner at 3:00pm and pooping 6 times before bed, she would still poop herself at least once, if not multiple times a night. We discontinued the fiber food, she’s back on Purina. The only thing that helped firm her stools has been “Bernies perfect poops”. She had normal stools for about 3 weeks but were now in another episode of liquid diarrhea going on 3 days, this time with lethargy the first day but still great appetite. X-rays showed no abnormalities. No change in food, still no treats, same routine. I’m beyond exhausted and discouraged from giving multiple baths in the middle of the night and would like any advice you have to give.