New waiter shoulder pain

Hey, I started as a waiter 2 weeks ago, and i work around 11-13 hour shifts.

We use trays to move The food around The restaurant, and i usually use my left arm for The tray while serving with my right.

And I’ve started to get really annoying pain in my lower right shoulder from it, and I was wondering if there was some exercise I could do to help minimize it? Thanks in advance!