welcome to Health care magic.
1.Possible cause could be ductal ectasia ( dilated ducts) as it increased after having baby.
2.Other possible the lesion has grown in the size.
3.If you are my patient i would have examined first and then send you for an
ultrasound breast, to evaluate the nature of the lump (cystic, solid,mixed), source ( duct, breast tissue,fat) and its extensions ( chest wall, vessels, ducts).
4.Depending on the findings - FNAC might be needed ( fine needle aspiration cytology)
5.Depending on FNAC findings operative or not will be decided. Good luck.
Hope it helps you. Wish you a good health.
Anything to ask ? do not hesitate. Thank you.