Left breast got bigger some lumps pain in breast got checked my doctor he said it could be fluid he said i shudnt worry now im getting pain in armpit?

? mastitis: This sounds like it could be a developing infection in the breast, called mastitis. Typically the lumps in the breast would also be painful, and there would also be warmth, swelling and redness. Watch for a fever. Alternatively, the lumps may be due to glandular or cystic changes in the breast. I would think with armpit involvement, your doctor may want to do further testing such as ultrasound.