Hi Op, hopefully this isn't the issue but the whipping the head away at EXACTLY the same amount each time is a tell tale sign of a bottle aversion. It usually stems from very well intentioned pressure to feed more on babies who happen to be extra sensitive to pressure. So then baby starts pushing back and refusing basically - they eat JUST enough to be satiated and then stop. My baby was one of these babies! it can happen for many reasons, but pressure is a part of it always (even though it is well well intentioned on our parts as parents! This part of it can be really hard to accept). Your pediatrician likely won't be super well versed in it.
My recommendation as someone who experienced this is to read a little about bottle aversion and then keep your eye on it. The first time I read about it I said oh no that's not my baby he's not that extreme. And then as time went on finally a lactation consultant said to me, oh that sounds exactly like bottle aversion behavior. The second time I picked up the book it all made a lot more sense. So, I have no idea if this is what your baby is going through but if it is it will likely get worse and so I want to share it so it's on your radar (because it can get so stressful!) because I am so so glad that the LC finally said this is a bottle aversion!
The good news is there is a very effective treatment. There is a book that walks you through it and you can also do a consult which I ended up doing and was VERY helpful. This is the book on it:
https://www.amazon.com/Your-Babys-Bottle-feeding-Aversion-Solutions-ebook/dp/B076PWRHH2
I can't get their website to work for some reason but here are the experts on it
https://www.facebook.com/Babycareadvice/