Six weeks old - awake at night. What can I do?

[Sleepglorioussleep]

Dd2 is gorgeous. She had been doing a stretch of four or five hours at night, followed by often being awake for two hours or so, but this was bearable because of the longer stretch before that.
Last night was, even putting a positive spin on it, pretty grim. She was asleep between nine and eleven, then awake for an hour, asleep til one then didn't properly go back to sleep til five. Then awake again at six fifteen and is just falling asleep now after a bit of dozing on and off.
I am not at my best this morning!! And I'm really scared of this becoming a pattern and the effect on my other two dc and dh.

What can I do? I had her in bed last night and dh slept elsewhere and I don't know if that made it worse as I fed her lying down and I'm not sure if I fed properly. Dh is certainly sure it didn't help.
Any words of wisdom? I'm not confident about my ability to instigate routine with dd2, because my resolve and ability to wake her up (she did sleep quite a lot in the day yesterday) go a bit to mush when I'm tired and weepy (a distinct possibility today!

She's having a developmental burst - interrupted sleep is pretty standard for them. May be worth checking that she is eating properly when you feed her in the small hours, rather than just snacking-and-napping. One thing you can be certain about is that it won't become a pattern! Small babies change their patterns randomly for months before working out their own routine. Take it easy today and see what happens tonight!

Thanks octavia! In theory I should know all this - she is number three! But the other two didn't really wake at night-they did but only to feed and then they were asleep and in Moses basket again. But it is swings and roundabouts because they did wake three hourly for feeds for months. The developmental spurt makes sense-head holding seems to have become hugely stronger in last day or so. And I'm sure I was less careful to do proper feeds when I was lying down with her last night. Here's hoping for better tonight!