Spit up/reflux - sanity check

My nearly 4 week old LO hasn’t had too much of an issue with spit up until this last 10 days or so, the last few in particular. She’s entirely breastfed and has had some issues with weight gain due to tongue tie and poor latch which have now been resolved and she’s quite a frantic feeder!

She’s now spitting up after every feed, often a large amount and occasionally the entire feed. Sometimes it’s immediately afterwards, sometimes hours later (despite keeping her upright for a while after and feeding in a slightly upright cross cradle position). She’s always been one for multiple feeds before she eventually settles last thing before we go to bed (obvs she’s not in routine yet), and the last few nights we’ve had to navigate hours of her being wide awake/feeding/spitting up/hungry again and repeat.

Yesterday the very unhelpful GP said she may be overfeeding (which I thought wasn’t really possible for breastfed). GP didn’t give us any clear instructions on what to try and fobbed us off (honestly the worst GP experience I’ve ever had for other reasons too).

Is that what’s happening here? Am I now suddenly misreading her cues and feeding her when I shouldn’t be? She’s refused feeds in the past when she’s been full so I’m not sure why should suddenly stop doing that. How can we get her to break the vicious cycle?