The description of your pain is an accurate description of the path of the ulna nerve.
The ulna nerve arises in the armpit from fibres from the spinal cord. And just like the description of your pain, runs down the arm to supply the little and ring finger.
I suspect that the main problem is a spasm of the chest muscles which is pinching the nerve at the armpit, especially since you say that the chest pain and numbness is brough on by stressful conditions. Stress can cause unconscious spasm of the muscles with pain being the prominent symptom.
It will be best if you were to contact your doctor. You will need Xrays of the chest as well as other tests like nerve conduction studies.
Other causes of chest pain like heart problems, gallbladderstones etc, though not very likely will also need to be ruled out.
If the pain is quite severe, you can take motrin 500mg for relief. Rub a muscle relaxant like Tobricin or Icy-hot over the chest muscles - relaxation of the muscles will also help to decrease the pinching on the arm. A wram pack ( a towel soaked in hot water and wrung out) for 10minutes every hour will also help.
I hope this helps.
Let me know if you need more input. If not, please click on the green"Accept" button on this page. A positive rating and adding a bonus will be warmly appreciated.