Thanks for the query to H.C. M. Forum.
You mentioned that itchy nipple ( particularly left) , please mention , whether itching more or less on both side.
If on both side than consider about ECZEMA
( if on other parts of body).
Painful swelling near armpit may be due to infection in breast itself .
Because central group of lymph
nodes lies at the apex of axilla
Sometimes axillary tail of breast may be mistaken for enlarged lymph nodes.
So consult a surgeon/ dermatologist
and get their opinion.
Hope I have answered your question.
If further any question I will help.