Another possible explanation

So all the books I've been reading about babies not sleeping start by saying "make sure nothing is medically wrong before undertaking any of these methods" and since some of the time when Kiernan wakes up in the night he seems to frantically upset I thought I'd better take him to the doctor just to check. She thinks he has reflux - which sort of makes sense given Eric had it as a baby and even gave himself a hernia from screaming so hard from it, and still sort of has it now. So, we're giving him medication, the equivalent to baby zantax and we'll see if it helps... last night he slept quite well from 7pm until 2 am but then was up every half an hour to an hour for the next 3-4 hours so.. it certainly wasn't an instant fix.
On an up note, he weighed 13lbs 8oz so I feel much better about him and him getting enough to eat.