One boob bigger than the other

This is kind of a silly question but here goes... I'm an FTM of an almost 3 month old, he is fully breastfed. I recently noticed that one of my breasts is bigger than the other and feels fuller. They were small but even in size all my life and throughout pregnancy. I nurse on both sides, starting each feed on a different side, so they would empty out evenly. I tried emptying out the bigger side first a few times, but I'm afraid it will only make that side fuller. If I work the smaller side more, the bigger one gets even fuller... Has anyone dealt with this? I know it's dumb to worry about this, I just don't want them to sag unevenly when I'm done nursing.