Are there any natural ways to increase breast size?

No pills... There aren't any pills or creams that are yet proven to give permanent breast size increases. Fat grafting does work - using your body's own natural tissue, but is a surgical procedure.
Get Pregnant. I can't recommend this as a long term solution but it will work in the short term. Seriously, there really aren't any good safe ways to increase the size of the breasts that use medicines, hormones or injections.