As a vet, I would say at a day and a half, having been on mum not a bottle, it's probably not bloat, but more likely watery mouth/water belly. This is an e coli infection and needs aggressive treatment with antibiotics, enemas, warming, electrolyte solution for feeding little and often and still often won't make it. I'd take it straight to the vet for help if you don't know what you're doing if you want it to survive.