Thank you for all the replies. She is 11 weeks old but was 7 weeks early. I considered that she may have reflux when she was in SCBU as when her feeds increased to fill feeds (via NG tube) she started having increased desats which is an indicator for reflux and is how DD1s reflux was diagnosed. DD1 was given medication for it - ranitidine and domperidone. I mentioned it to the nurses but there is a different neonatologist from when DD1 was there and while all premature babies used to be on reflux meds (they're more prone to it from having the tube keeping their oesophagus open), the new consultant has a different approach and only prescribes meds in the most severe cases.
Obviously, as I have DD1 sleeping in the day isn't a possibility either. My one saving grace is that she does sleep at night but that's either on my chest or next to me and co-sleeping isn't recommended for premature babies.
As for feeding she is fully breastfed. I do worry that she isn't getting enough because I had to establish my supply by expressing and it took about 3 or 4 weeks until she was fully breastfeeding. But since then she has been gaining weight and she does have plenty of wet and dirty nappies.
She does have colic - whatever that is! She screams/cries from about 5 to 9pm every day and I wonder how much of that is down to either being hungry or being overtired, but she cries and pulls off when I try to feed her and she really does seem in discomfort. Usually she will cry and cry and cry until she does a poo and then she will start to settle down.
In terms of routine there is none! Although she's 11 weeks she's still less than 8lb so she is basically like a newborn. As a generally idea this is what our day typically looks like. She does consistently have a feed at 2am and usually another between 4am and 6am, but from 8am onwards she feeds on demand and it can be pretty much constant for most of the day.
When she was in SCBU she slept in her incubator no problem. When she moved to an open cot she was unsettled at first - I think the lights and the noise bothered her. When she came home from hospital she would sleep in her cot, sometimes for a couple of hours. Recently, the longest she has slept in her cot is half an hour.
I really wish that she would sleep for her own sake. She's just so unhappy when she's awake. I feel so bad for her.