Thanks for your query,based on the facts that you have posted it appears that you have tender nipple with enlarged lymph
node in axila.
This could be a primary infection of a nipple or staphylococcal infection
of a hair follicle (Boil) near nipple.
You need to take broad spectrum antibiotic like Cefexine along with anti inflammatory drug like Diclofenac
Do not worry this will get cured within a week.