One breast is WAY larger than the other.

My breasts are C cup, and I'm 20 years old. I've taken pictures of them to send to my husband for years now. Last year, they were perfect. I had the plastic surgery look, without plastic surgery. Lol. Well these past few days I've noticed that my right one has a BIG size difference from the other. They've always had a minut difference, but never this large and noticeable. Is this normal? Does anyone else have this problem? Is there anything that can be done to correct it, exercise?