If it's painful, see a gynecologist immediately, as this can be a serious condition if untreated.
However, it's much more probable that one
of your lips
is simply larger than the other. There’s nothing wrong with you. You’re fine. Realize that everyone is different. Vulvas are like noses: Everyone has a nose, and they’re fairly similar; however, there are small variations. Some noses are pert and tiny, while others are more imposing. But they’re all noses, just the same.