Our ds of 6 months has always been a great sleeper until recently...and I am now more tired than I was when he was a newborn! Sorry about the long story below, but hoping that someone might have some ideas...
He slept through from about 3 months, probably because he is quite chunky and was able to take in the required amount of food to get him through the night.
At 5 months he started waking once or twice a night - didn't seem to want anything, but usually settled quite quickly if we gave a dummy. He seems to use it to massage his gums 'cause he was drooling and struggling with the gums during the day.
At 6 months he caught a really nasty cold which he has only just got over (been better for a week). He didn't eat well during the day when he was sick and other than waking because he had a temperature he did regularly take in food and water at night.
He is now waking up at least once during the night for a bottle and he will not be settled by a dummy or water (in fact he seems to have given up on water altogether!) We tried giving him a half bottle and that just seems to upset him and he complains until he has had the whole lot. He usually isn't a greedy baby - he knows when he has had enough. In addition to this he wakes up another once or twice when it is possible to settle him with a quick cuddle or a dummy.
When he wakes we don't talk much to him, we keep the lights low and we always try water 1st.
Our ds is on 3 meals a day and 4 full bottles and sleeps about 2.5 to 3 hours during the day (2 short and one longer nap). His food contains dairy and occasional meat in attempt to increase the calories.
Has he got into bad habits from being sick (but he was also waking up before he got sick), can it be a growth spurt (how long do they last - it has been a week?) or could it be teething (been drooling and chomping for 3 months with no sign of gnashers!). Heeelp?