Does know exactly what part of my arm hurts when I stretch it too far to reach for something or if I take my coat funny?
I know this is hard to describe, but sometimes I get this sharp, but brief, pain in my upper arm from time to time. It goes away after a minute or so, so I assume it’s some sort of a muscle spasm.
IANAD, but my father is…
…at any rate, wouldn’t that be the triceps, the muscle responsible for extending the arm, and the complimentary muscle to the biceps?
If it is in the upper arm then it is possibly a shoulder injury with referred pain. See a doctor, though most injuries of that kind generally heal themselves. All a doctor will do is confirm that it isn’t something more serious or something that can be treated like a spur.
I get that too. people probably think i’m nuts. does the pain come for seemingly no reason? like you are just sitting there and there is a sharp shooting pain through your arm for like a few seconds?
one of the signs of heart trouble is shooting pains in the limbs, but lots of other things can cause that too. Your best bet is a doctor - online consultations are somewhat error prone
No, it’s not referred pain or anything like that. It’s definitely something I get from stretching my arm out too far. I suppose that a muscle gets stretched a bit too far.
I’m enough of a hypochondriac to know about the “arm pain as sign of heart attack” 
An example of this pain would be when I reach over the front seat of my car into my back seat and then “OUCH!”. It’s almost always in my upper arm.
But the pain goes away after a few minutes.
I suppose the cure for this would be, “Then just don’t do that.”