@jasperr I know vets often recommend chicken and rice, but our old pup (passed away at 14 after a battle with other illnesses) had a sensitivity to chicken. Just chicken. Anything with chicken, chicken meal, chicken flavour... it seemed like he'd get diarrhea if chicken had ever been in the same room as his food. This did not apply to any other poultry product - he was totally fine with duck, turkey, eggs, and pheasant.
We used pureed pumpkin with rice. Just some tablespoons of the cans of pureed plain pumpkin with some fresh plain white rice firmed it up pretty quickly. Or, if his poop was just soft, not liquid, a tablespoon or so of pumpkin on top of his regular food (Orijen Six Fish). When he was on antibiotics, we'd give him some plain Greek yogurt along with the pumpkin on his food to help avoid any diarrhea.
Obviously this should be canvassed with your vet, but that's what worked for us and it may be worth a conversation if the panel comes back negative.
We use Nylabones as the primary chew toys for our 3 month old pup. Others here had great suggestions too for chews that aren't food based.
I'm so sorry to hear you're having such a rough go of things right now. I wish both you and your pup the speediest of recoveries. Give your pup a scritch for me!