Hi,
I completely agree with ladybirdgal.
Unless you have other symptoms,like itching,nipple inversion and discharge,redness,pain and skin changes,then don't worry, different sized breasts is perfectly normal and it's quite common.If you are very young, this difference in your breast size will probably even out, usually by age 20 or older..
Every woman is different and no two women's breast will look exactly the same even when fully developed.If you're really worried about your breast size, make an appointment to see your family doctor who should be able to reassure you that your breasts are normal.
Take care....
Most women's breast are not symmetrical, most having one breast slightly larger than the other. But if you have develop an increase in size that is a change from your normal size you should definitely seek medical advise. If you have any of these symptoms redness, soreness not related to menses, hard lumps or bumps, indentations, discoloration, nipple discharge, or others that concern you, you should see your doctor.