I think you might need to switch doctors because as a mom and nurse, that's concerning. Excessive drool isn't normal after 1-2 yrs old. I'd maybe take him to an ENT and get speech/OT involved.
Super concerning. Please switch doctors and get referrals to feeding therapy and OT
Does it seem like his mouth is in pain? Maybe take him to a dentist and see if there is something abnormal going on with his teeth. Really though, even if they're not concerned about drool, his doctor probably should be concerned he's not eating solid foods. If he's not eating solid foods, it might be hard for him to go for long periods without eating/drinking (thus being fussy). Even if he gets enough total calories during the day, he might be consistently hungry between meals because the food goes right through him. Does he poop ok? That might also be a source of discomfort...