In theory, a lo should be able to sleep all night at that point. My first thought is maybe not enough calories during the day/evening? How is he doing on solids? How long dose he nurse at night? My instinct tells me that it would be an easier process to help him go back to sleep during the night rather, than the frequent wake/cry/ sleep. That would just cause all kinds of upset/ set up for overtired. Hopefully one of the mommies with an older child will have more ideas, mine is no where near the point of sleep all night. Other places to check are the prop board, if he is using you to go back to sleep. And PU/PD to helps teach self soothing stuff.