2x breast reduction 97, 05. numbness r breast since. now 18/40 pregnant and lump found. well defined, 2cm, painful on palpation. potential differentials?

At your age: The lump is most likely benign. However a biopsy would be required to be sure. Often a needle biopsy with ultrasound can get you an answer. Good luck.

Breast lump/pregnant: Fat necrosis is the most likely, but could also be fat/oil cyst, or breast tumor. In general, cancer lumps are not painful. Nonetheless the mass can be diagnosed with a fine needle aspiration and/or ultrasound. Get to a breast doctor asap. Good luck on your pregnancy.