Dog has had diarrhea for three weeks on and off. Vet out of differential diagnosis

My dog is 4.5 years old, male , Taiwan dog, previously on raw diet, neutered, presently 19.6 kg. He has been suffering from diarrhea on and off for three weeks. Has already had 2 rounds of antibiotics treatment. First round + anti-diarrhea meds and he didn't poop for 5 days. As soon as the antibiotics were over the diarrhoea returned. Second time vet added 7 days anti-biotic course + folic acid + intensitine motility meds because in X-ray he saw food was not moving from stomach and there was gas in small Intenstine. Once the meds started he didn't poop for 9 days. ( We moved him from raw food to boiled chicken and broth during second round of meds). His first poop was semi-solid but after that diarrhea is back. His appetite is good, I feel he's a little more hungry than usual. We added pumpkin when he wasn't pooping. The diarrhoea is accompanied by mucus but no blood. Doctor has ruled out obstruction as no vomiting. No giardia was found in fecal exam though excess bacteria was found in stool which was cleared after second round of antibiotics. Ever since this started he has lost about 2kgs weight. Anybody seen something similar? Vet is out of differentials. His CBC reports are good. Last 2 X-rays was also good. No warning signs there. We are desperate for help. Thank you!