My left breast was always a little bigger than the right but recently i have started noticing considerable difference. no lump, normal nipple. reason?

Breast asymmetry: We are all a little asymmetric- change could be weight related.

Unequal development: Some times both are not exactly equal size, due to unequal development, or injury during child hood etc , don't be self-conscious about this , in order not to look conspicuous padding the braw may help you or seek the help of a plastic surgeon , variety of methods available