Firstly, thanks Emma, I did log on earlier, but only briefly and would have missed this one.
When he has the night wakings, are they consistent for a few nights, or just one offs here and there. Can you try to tell me what the picture has been say for the last fortnight, ie how many night slept through, how many nights crying, how many nights easy to settle back.
Also, when he is crying and crying, what do you do, how long does it go on for and what gets him back to sleep eventually?