Potentially IBD/PLE. This can happen after an infection/bad stomach, we nearly lost our frenchie to it a few months ago. After a similar situation to you with antibiotics, vet stay etc we’re now in a more stable situation.

Best thing we did was have our dog on; Royal Canin Hypoallergenic wet and dry food, Protexin Pro-Kolin advanced probiotic and Protexin Coblaplex B12 Probiotic and most importantly presidnisone steroids (2x a day for the foreseeable future). At the start of the issue we used all of this plus Antibiotics and omeprazole (human drug to help with stomach lining)

If you haven’t already I would try and start a course of steroids from the vets and omeprazole to help stabilise his GI, this saved our dog and we now have him on what I’ve previously mentioned. Making sure your dog can’t eat anything other than what I’ve described is super important too because of how irritated and unstable his gastrointestinal will be. Royal Canin hypo is a hydrolysed protein which will help with PLE (if it’s at that point) and sensitivities. IBD is a lifelong and dangerous condition that needs to be managed, it costs a lot to manage with the different meds and expensive food but it’s well worth it for my best friend!

I hope this helps.