Why is under my left armpit & breasts sore

Hi Anon

Thanks for your post! 

Underarm pain can be caused by many things including ill-fitting clothing, medication side effects and more. They are also sometimes caused by a virus, probably harmless and you'll feel ok soon. When we have a virus, our lymph nodes sometimes swell. We have many nodes in our arm pits so this may be what is going on with you. 

If the pain continues after you feel better, see your doctor, but I suspect it will subside when you feel better.

Hope that helps,

Pam