I had my last regular period in Oct '04 and got preg with my first child in Dec '04. I have had another child since then and breastfed them both for 9 months each. I have had 10 periods total in 6 years and my doctors do not know why. I am healthy, my hormone levels are fine and I have not been on any birth control since '03. I just do not have to buy tampons very often. Other than some difficulty getting pregnant, (because I do not know when I ovulate) I have had no physical problems with not menstruating every month or even every other month.
So I would say to just enjoy it unless you start to have other problems.