Most woman do have breasts that have one breast grow a bit bigger than the other and it's usually a normal thing and nothing to worry about.
Your breasts grow as a result of water retention and blood flow and when one of your breasts has more blood flow and water retention than the other then you can have one breast bigger than the other.
Even my breasts are not exactly the same in size and my left breast is a bit bigger than my right breasts and I spoke with my doctor and she said that it was a normal thing and nothing was wrong.
But if your breasts were the same size before and suddenly you notice one breast larger than the other then you might want to speak with your doctor about it just to be safe.
But most woman have breasts that are one size larger than the other and nothing is wrong.