What Causes Pain In Armpit Radiating Towards Palm?

I lately feel some mild pin under my left arm, actually right in the arm pit. I nticd it first a few weeks ago when I woke up in the middle of the night to attend to my diabetic son. It is a radiating sensation that now travels down into my left palm. Is this worrisome? Which type of doctor should I see? ... It has been an extremely sressful last year so no surprise I start aching a bit. Less exercise, sleepless nights .... Thank you!