one boob bigger?

Bianka
I know 'everyone has one boob bigger then the other' but are they really that different in size 1 boob is a cup bigger? 
The past 2-3 years my left breast has been bigger (more tissue) then the other. Iv asked a specialist, doctor, dietitian about it and they don't say much about it beside 'everyone's got one bigger then the other' 
Anyone else have this issue?