Welcome to you and your parakeet! What's his name by the way?
What you are observing may be your bird adjusting his crop. That can look like an exaggerated yawn that may continue for a few minutes. A video might give us a better idea for sure if you can upload one? Easiest way to do that is upload a video to YouTube and link it from there.
We love birdie pictures here too so this may help you upload those...
I've seen my Budgie do that sometimes, but not often. Your bird may be trying to move around some food to swallow better, or simply stretching it's beak and muscles. Have you noticed any drainage from the nostrils, or shaking the head while expelling some food? That could be signs of a sinus infection.
Where I live sometimes the air is pretty moist or thick with allergens, and that may cause a bird to try to draw in more air, kind of like what we do when short of breath. Your bird could be trying to "pop his ears" if the air there has a lot of high pressure.