From what I understand, stress could be the cause of all kinds of things, including hair loss. I'm not sure about specifically armpit hair- but I would guess that it might be possible.
Regardless, with something like that it's hard to tell the real cause without seeing a medical professional- so that's what I would recommend doing as soon as you can. They will know if additional tests are needed and have a better lead on what the cause is. If it's a skin condition, stress, or something else.
Let us know how you are doing after you see your doctor!