This swelling in your armpit could be a sebaceous cyst, lipoma (benign tumor) or an extra breast tissue.
If this is a swollen lymph node, it could be an initial sign of lymphoma or breast cancer (sometimes breast cancer changes can affect the armpit lymph nodes before the breast it self).
Since you have this bump for two years it is most likely something benign, but, it is very important to be checked for lymphoma (lymphoma can go unnoticed for long time, just giving swollen lymph nodes in neck or armpit accompanied with not specific symptoms like fatigue, feeling moody, low grade fever, loss of weight, night time sweating).
The description of the mole indicates need for a dermatologist's visit.
Using a dermatoscope your dermatologist will know if this mole is suspicious or not.
Ask your physician for a regular blood count test and it will be a good idea to get the armpit bump biopsied or cut off.
Best wishes!
Marija