What Could Be The Reason For Having Tender Localized Spots In My Armpits?

I have had very tender localized spots in my armpits for many years (I'm a 55-yr-old female). Doctors have told me repeatedly that I shouldn't worry about it--may be cyst (but I was ultrasounded and no cysts), may be related to menses (I am post-menopausal now). A holistic practitioner thought it might be lymph blockage (but several drainage treatments did not make it go away). There is a general puffiness to the whole area sometimes, but no discrete lumps. Any ideas?