Thanks for posting you query.
Asymmetrical/uneven Breasts are common cosmetic problem caused by breast feeding.
It can be surgically corrected but still you have other choice to go with:
One is to massage
the smaller breast.
Breast enhancement pump can be used.
If one breast sags more than the other, a condition called Breast Ptosis
, a Breast Lift or Dermal Mastopexy
can be done to lift the breast to match the non sagging breast.
Hope it helps.