Sounds like it could be my post exactly! This has been going on for the last two weeks :-(
I have no answers as nothing I try is working, getting him to sleep is easy but keeping him asleep is not!
The only thing I do now to make sure the other two aren't being neglected is put him in my hug a bub do my hands are free to help them and he gets an hour sleep!
It's doing my head in but I believe it will pass soon enough....well I tell myself that or I'll go cookoo......................