Oof, I wish I knew. I'm having EXACTLY the same problems with my five-month-old, and have been since about 17 weeks. (See my thread 'WTF is going on with my four-month-old down the list).
It's so frustrating isn't it. Just when you think you have it cracked, they go and change entirely.
I've tried doing a dreamfeed at 11, but the main result of that seems to be he'll do a gigantic pooh at around 2, so I have to get up anyway and feed him back to sleep. Last night he fed at 11, then woke up at 2.30 hungry. But then slept until 8, showing he can go 5 or 6 hours between feeds. But other nights he wakes up every three hours or so, and I don't know if he's hungry or just awake, so I have the same dilemma about whether to take the easy option of feeding him back to sleep.
Some have said to give him solids, some have said it would be counter productive as he'll then not have room for the milk.
He's BF, but gets very distracted during the day, so maybe he's not getting enough.
He's not a great napper during the day, and I'm not sure if that's part of the problem, but I'm beginning to feel totally inadequate. What with that and the sleep deprivation, I get a bit short with DS sometimes, which makes me cry with guilt.
So, in short I feel your pain!