GERD with exclusive breastfeeding VS something more serious?

My DD is now 3 months old and exclusively breastfed. After her first few weeks things got difficult with breastfeeding- she would only nurse for 5 minutes, she would cry and arch her back, if she fed longer than 5 minutes she would projectile vomit the whole feeding, sometimes a previous feeding cuddled. She got to the point where she would vomit her entire stomach contents 3 times a day. Her weight percentile dropped from 80s to 40s. My ped thought something was wrong with my supply but she was wrong- I was able to pump off over 2,000 oz in two months, my supply is great and her latch and everything checked out and was given the thumbs up by a lactation specialist, though she only eats 2oz at a time and never more than that.

We preceeded to begin treatment for GERD. Her vomiting did decrease to only once per week but her feedings remained very short though she did start gaining weight and steadily rose to 50s percentile.

Now my first kiddo was a tubby booby baby her entire infancy- drained both boobs like champ and fed for 15+ minutes total. I figured my newbie maybe just liked short feeds every 2 hours and that's just how it was gonna go.

But she is starting to WANT to feed longer and wait longer between feeds. Tonight she wanted to drain both boobs after 3.5 hours between feeds (she refused when I offered at the 2 hour mark) and unfortunately the picture was the result of that 20 min feeding and I'm very frustrated. I'm told it's not possible to 'overfeed' a breastfed baby, that they will stop when they are full. So why is this happening when she finally wants to feed longer than 5 minutes or take in more than 2oz?

I'm aware that pyloric stenosis is usually discovered early due to weight loss and dehydration symptoms and her being a seemingly happy and healthy 3 month old doesn't seem like it would be a cause for concern but I really wonder.

Does anyone have a similar experience? She acts like she wants to eat more but everytime she does this happens. My pediatrician hasn't seen this photo yet but she is very apprehensive to suggest any more interventions over "a little spit up". I don't think she believes me when I say HER ENTIRE STOMACH CONTENTS. My baby is currently on famotidine, which like I said helped with the multiple instances of vomiting but doesn't help increase my baby's intake, which makes me believe something different might be going on to prevent her from intaking more than 2oz at a time?