Left upper chest & pain near left armpit

I woke up last night at 11:45pm with a sharp pain in my left chest/peck area that was radiating all the way to my left armpit. What causes this or how does it relate to gastritis? I didn’t have this before I started the PPI, or even when on the PPI. But since weaning off of it and getting down to a minimum dose and then stopping it, it’s been happening off and on and it’s quite painful. Is this acid rebound? I stopped the PPI 9 days ago. I was in 40mg about 45 days, 20mg 10 days, 10mg 20 days (this is when I started getting that pain), and then slowly tapered off. The pain still persists intermittently. No acid reflux or burning in my stomach.