Sounds right re sucking however she may only be getting foremilk which may not fill her.
My DD did the same and it took a bit of taking off/back on to get her to keep going. My DD is a lazy eater!
As for the sleep, it could all be connected but this phase shall pass once your DD gets the hang of feeding.
BF is hard work, requires commitment, but don't feel bad or guilty if you make the choice of formula.
I was advised by a MW and LC to give formula top ups due to weight loss, late and low milk supply and DD being unsettled. Basically we now only use it IF she seems unsettled and hasn't drank much, but I've now been able to give her BF top ups as my supply has increased. At the end of the day, I figured its not dangerous (it wouldn't be sold if was!) and if DD was putting on weight etc then why should I feel bad??
You are doing great, and remember it all doesn't last forever!