My twins are 16 weeks tomorrow and having been doing the same as you describe in your post. Mine have never really been good sleeper but now they are even worse, they use to sleep from their last bottle at 10pm to about 3-4am now they only make it until 2am and are unsettled until their 6am bottle. Then when they do get their bottle they just play with it. My son also was a good drinker and would gutz his bottle, now I have to force feed him to get him to drink half of it. I have had them checked by the doctor and there is nothing else wrong with them and they really wouldn't comment about whether it was teething or not.