Trying to transition from bottle of formula to sippy cup of milk during the day seems to be messing with my 13 month olds sleep

When I first tried giving my son whole milk in a bottle a month or so a go he made a face, let it dribble out his mouth and pushed the bottle away, so i went back to formula. I tried again this week with milk in the sippy cup and he did a lot better. He'd drink some, pause, drink some more. He wouldn't down a whole cup at a time like he would a bottle of formula but when he seemed done I'd just pop it in the fridge till he wanted more and through the course of the day I'd estimate he had about a cup and a half of milk. When he was taking formula he'd take 4 half cup bottles through the day, so not quite as much but I figure he's still getting used to it and would increase his intake on his own eventually.The thing is the last three nights since i started trying to transition him he's started waking up wanting a bottle around 1-3 am again. For the last month and a half or so he generally slept until 4 or 5, had a bottle, then slept for another hour or two, and more recently, occasionally sleeping all the way until 6.He's a great eater, 3 fairly solid meals and two snacks a day. I try to make sure each meal has protein and healthy fats to fill him up so his calories should be fine. I wonder if he's waking up thirsty and I should try encouraging more water but I also worry that will end up cutting back on his milk intake even more.Should I try offering him more water during the day? Try a few days off just giving him water when he wakes up at night? Just accept having a few nights of rough sleep and cut him off overnight? I'm not totally opposed to letting him cry, it's just hard to stick to it when the options are, let him cry and be awake for potentially an hour or more (and maybe even be woken up again later in the night) or take the 10 minutes to give him a bottle and go back to sleep the rest of the night) via /r/Parenting http://ift.tt/2aAyUeM