Hi D.,
This is what came to my mind. First how many times is he waking up at night? Do you have a routine that you do with him each night? I am asking because I am sort of in the same boat with my 3 month old. I am trying to get her on a night time routine and have been reading upon it, because she is literally up all day, barley naps, and she is not going to bed for the night until 11 or 12 at night and only sleeping 3 hrs then getting up again etc.. it is wiping me out as well.
So I just started this with her, each night pick a time that is suitable for you, do the same few things with him so he will get in the habit of knowing that it is going to be bedtime, such as putting on jammies, rubbing nighttime lotion (they have nighttime soothing lotions) reading the same story so he will get familiar with it. I have been using the Ocean Wonders music box that you can attach to the crib or it stands upright, it plays soothing music and has a dim light and makes bubble noises, she loves laying there looking at it and watching the fishes in it. I lay her on my bed do all of the above while I have the Ocean Wonders sitting right next to her playing the music, although it has different "songs" i have been sticking to the same one every night so she will get use to it. I try to let her lay and fall asleep, but I have to rock her or pat her more to get her to fall asleep then i put the Ocean Wonder in the crib just in case I have to use it throughout the night. I just recently saw in a store ad that they have something similar to that for the crib but it has a remote control so if the baby wakes up instead of you running in there to turn it on (and they see u and end up waking up etc..) you can just push the remote to turn it on without disturbing them.
My results so far since this is new for me with her, she has been sleeping through the night and getting up 2-3 times to feed but eats and goes right back to sleep, there have been a few nights where she was up all night etc.. that will happen, so be as patient as you can.
Just try to keep a routine going and maybe he will find comfort in that. Being that he is 7 1/2 ms if he take a "binkie" leave one in the bed for him- the Ocean Wonders thing has a big button that they can tap themselves to turn it on, my sister has a 6mth old and she has one in her crib, and can activate it on her own.
Nothing against your doctors opinion, but I have NEVER heard of giving a baby a water bottle?? And since when is there a set age limit, especially with babies they are not robots. Doctors are all different and have their set opinion, just hear what they have to say, but go with your gut instinct, your the one that is with your baby all the time not them so don't take everything they say too seriously or feel pressured to do what they suggest.
Babies will do things on their own pace it does not sound like an eating issue, sounds more like a comforting one. He may just need to feel more secure on his own try to get him into a routine and see what happens.
Sorry for the long response, I hope my advise will have some use for you. Best of luck!
A.