Left breast swollen and sore for two months.armpit swollen to.drs can't figure out y.breast ultrasound normal.what's wrong and what's next?

?mild mastitis: Could be mild mastitis, not seen on ultrasound. Continue to get evaluated by your dr. And possibly lab work to assure not infectious (cbc, etc), warm compresses and empiric treatment with antibiotics may do the trick, but you need your dr. To evaluate you and decide on best course after examining you. Good luck.

Many things: Can cause your symptoms. Fibrocystic disease, infection and other entities can present this way. Primary breast cancer however is exceptionally rare in women your age.