Breast and nipple pain, recently found a lump under my left armpit. my menstrual cycle is coming up. is there cause for concern?

Breast pain: Breast pain is common during and preceding your period. If the lump in your axilla (armpit) doesn't go away after your period you should see your doctor. He/she would likely prescribe antibiotics. If the lump doesn't resolve after 2 weeks of antibiotics i would suggest an fna (fine needle aspirate) to obtain cells which are examined by a pathologist.