The thing is, she is only 6 weeks old. She has a tiny tummy that needs filling regularly, the amount she is waking for feeds in the night is totally normal - she is going 3 hours or more between feeds, given all the problems you have had she is actually doing well. My DD was born at the weight your LO is now and she certainly didn't do less night feeds for a long time, they do need the feeds.
If cluster feeding has made her puke more it probalby will again until she is a lot bigger and I doubt she is physically ready to take bigger feeds that will get her to sleep longer yet. If she's not drinking much at the DF you could try stopping that and wait for her to wake by herself, that may make a difference as she may wake between the DF time and the first NF time and then go 3/4 hours from that feed.
I know it's not what you want to hear but I really do think she's too small to be trying to alter her feeds right now, I think you need to ride it out until she starts to go longer stretches by herself.
Laura
