I had that same problem at 7 months. My son slept through the night from about 4 months on, then all of a sudden he kept waking up and he seened as if he really needed to eat. We started feeding him more baby food at dinner and gave him a "snack" of yogurt right before bed. That helped - the poor little guy was just hungry.
When he was almost one he had an ear infection and started waking up again at 3 am. When the infection gone he was "used to" that 3 am nursing; at that time I nursed him 1 minute less each night and after a few nights he was sleeping through again.
Good Luck - hopefully you will get to sleep again soon!