The Metronidazole is an antibiotic and will clear any infection from the gut. It can take about 10 days. The Sucralfate absorbs everything in their stomach. It is used to treat Ulcerative stomach. The Pectin is just a soother. It is given for Diarrhea, but doesn't always work. Ask your Vet to prescribe you some Forti-Flora. That will get the right balance going back in your babies gut. I wouldn't give any foods other than his normal dog food, and provide a bit less than you usually do. Too much food can irritate the stomach as well.
Are you giving the Metronidazole 1 hour before the Sucralfate? Sucralfate should be used 1 hour before, or after any other meds or food.
So many thing can cause bloody, mucusy diarrhea. Anything that disrupts the gut. Even things as simple as table food, or overeating. Worms, viral infections…. I’m guessing your vet did a fecal floatation? Most times the Vet will treat symptomatically unless it continues, then they will begin blood work. I hope your baby gets much better soon. Try out the Forti-Flora.
You can also try a boiled chicken & rice diet for 2 days. No salt. If it continues I'd try a diet change. Maybe something in the food he is eating is bothering his tummy.