I have one breast larger than the other. I have the A cup size, but it is big for my smaller breast.
I am 19 years old and my breasts had stopped growing long ago maybe when I was 16.
And I am wondering would it grow back again?

It is VERY normal to have one breast bigger than another.

Yep very normal. I also have one larger then the other. Look at it this way, your boyfriend/husband will have the best of both worlds.

Normal, very normal:)

If you find it real awkward, you can just put pads or undergo augmentation on the other just to balance it.

Yes normal. As far as them growing- Breasts do get bigger from weight gain, pregnancy, and some birth control pills. I've also heard of people doing exercised to increase their bust.

I Must! I Must! I Must Increase My Bust! - Fitness - Families.com (http://fitness.families.com/blog/i-must-i-must-i-must-increase-my-bust)