Uneven size- normal and don't worry.
BUT if you are seeing changes in the shape or size of your breast, you need to get a breast exam to rule out cancer (according to webmd) since you are old enough where it doesn't seem to be due to puberty or any hormonal changes.
web md says:
"Early breast cancer is often seen on a mammogram before there are any symptoms. The most common symptom of breast cancer is a painless lump. However, sometimes painful lumps are cancerous. Other symptoms of breast cancer include:
* A lump or thickening in the breast or armpit that is new or unusual.
*
A change in the size or shape of the breast.
* Skin changes, such as a dimple or pucker in the skin of the breast.
* Discharge or bleeding from the nipple that comes out without squeezing the nipple (spontaneous discharge).
* A change in the nipple.
* Scaling or crusting of the nipple.
* A change in the color or feel of the skin of the breast or the darker area around the nipple (areola).
* A breast lump in a man."