Posting in the hope that someone might have a magic cure for us 
Ds is seven months. He hardly sleeps now. At all. In the past few weeks we've reached a new low of waking every 45 minutes through the night. Sometimes he's wide awake and bawling but other times he's crying even though his eyes are shut and he seems otherwise asleep.
I'm almost at the end of my rope. I got more sleep when he was 2 weeks old. In fact by the time he was 6 weeks he was sleeping 9pm - 3am, had a quick feed and went straight back down til 6.30. It was great. Things went a bit funny at 12 weeks and by 16 weeks the 4 month sleep regression hit and night times have been hell ever since. He has been waking every 90 mins or so for the past couple of months, now it's every 45 and I just can't cope anymore.
We've got a good little routine going at night bath (which he loves), into grobag, bottle and into cot. This part goes fine but then 45 mins later the wakings start and go on til he's up for the day at 5-5.30. He does have reflux but its well managed with ranitidine and he's been treated for it since he was teeny. We still have the cot raised slighty with Argos catalogues as well just in case 
he also has a dummy which is generally what gets him back to sleep through the night but he can't do that himself. Have tried comforters etc but he's not interested.
Dh thinks we should leave him to cry but I'm not comfortable with doing that. I'm meant to be going back to work in 6 weeks and I don't know how I'll cope. We're just so so tired, it's beginning to affect our marriage. Hoping someone has some advice or something else we could try.