Sounds like a hernia. When your stomach muscles become week, they allow some of your internal organs to protrude which can make your skin bulge out and it may look "fatter" on one side. A hernia can be painful and sometimes dangerous to your internal organs. See a doctor for a proper diagnosis.
Different bodies are different - it could be that that's just how your body gains weight. Also, if you exercize the muscles on one side of your body more than the other, that could cause fat to build up on the other side.
It could be a lot of different things causing it but if it is concerning to you then you should get in and see your doctor they will probably be able to examine you and give you a diagnoses. You can also call the office and tell them the symptoms and they will know what to do.
While the body tends to grow symmetrically, this is not always the case, especially with fat. If you think this is something to be concerned with, see a doctor.
