Newborn sleeps but will not feed

[KJM2013]

My 2nd DD is 10 days old, she was born by section at 40 weeks weighing over 9lbs. By day 3 she had lost 12% of birth weight.
She never really got past the sleepy day one phase. I wanted to exclusively BF but she was never hungry and impossible to wake.
We were sent to hospital for 24hrs (blood test showed low blood sugar and slight dehydration), and I was on a constant cycle of trying to bf, express and top up by cup.
She had gained a little in 24hrs, so they sent us home to continue this regime.
By day 7 we had her 50% tongue tie snipped which gave a small amount of relief to my now bleeding and v sore nipples (latch so bad I was screaming sometimes).
Only seemed to gain weight when we got home with top ups and I was struggling to express much, so couldn't always top up.
Made the decision to introduce formula, a bottle, buy an Elvie pump and bottle feed with as much expressed milk as possible.
However, she is still so sleepy (easily goes 4-5 hours) and when she does feed has 2-3oz max.
Midwifes don't seem to be that bothered as there is some weight gain, albeit a few grams.
I'm worried something else is up, anyone with similar experience?

I don't have this experience with my son but know my mam had this exact problem with my sister. Apparently she was just not interested in eating and would happily sleep all day. My mam had to wake her up to feed her (exclusively formula fed) and even then she would suck at the bottle two or three times and not want anymore. I remember my mam waggling the bottle around in her mouth desperately trying to get her to drink more. She was underweight for the first two years but eventually caught up with her peers and put on some puppy fat in primary school. She was always a fussy eater though and even now as an adult eats a very limited variety of food although she eats massive portions. If the midwives aren't concerned and if she is gaining weight I don't think you should worry too much. I'm sure the midwives have seen plenty of other babies doing the same who have turned out alright.

My first was exactly the same he was a nightmare to feed, even when he became more wakeful he would only take a few ounces at a time. Even when he was 1 the most he could take in one bottle was 6oz, if he had a drop more he'd vomit it straight back up! I think he had a small stomach. He's still very lean now at 6, and only ever grazes.