It could be either. Did you start right away with doing that with every bottle? We started just adding in half cow's milk and half formula in one bottle each day, with the other 3 being formula, then went to one bottle a day of milk and the rest formula after a week, and then slowly over the course of a month and a half moved up to having one extra bottle of milk each week until all four bottles were cow's milk. So to start, she only had about 3oz a day of milk and the rest formula, and then the next week it was 6 oz a day of milk, and so on. I did notice a bit of unsettled sleep and also bad acidic poos, but she happened to be teething at exactly the same time, and that happened every time she teethed, including at 6 months and also when she got her molars later, so didn't appear to have anything to do with the milk. Once the teeth came through, everything settled down again, so I assume it was teething. Any chance she could be teething? Mine definitely would wake every 1-2 hours when she was. Also, that is a key time for separation anxiety too. Mine had it a bit earlier so was mostly done by then, but she was definitely waking lots during the night, same when she was trying to stand and walk. So it could be a number of those things. How are her poos? Are they the same or do they seem off? You could always slow down a bit if you do think it's related to the milk. Unless she's obviously in tummy discomfort, I would assume it could be any number of things and just slowly keep proceeding and see if it passes.