Hi,
What is your age? What symptoms are you having? Do you notice any abnormal features on breast self examination like a lump, nipple discharge or skin changes etc?
Do you notice any lumps in the underarm region?
The pain could be due to trauma, injury, tight clothes, bad posture, lifting heavy weights, infections of the lymph nodes etc.
You could try some warm compresses and oral pain relief medications and see if it helps with your symptoms.
If the pain still persists, it would be best to consult your doctor about this.
Let us know how you are doing and what your doctor advises.
Post us if you have any other doubts.
Regards.
It's always reasonable to go see your doctor for pain, since their exam is different from your own touch.