As the header says my teeth are getting yellow'ish to look at and I want to know why as I used to have nice white teeth. I'm 28, I do a lot of exercise and eat very healthy so the yellow teeth thing isn't working out for me.

Never smoked.
Never drank coffee or tea.
Rarely drink anything but water.
Brush my teeth for two minutes morning and evening.
Get my vitamins every day and blood test showed above normal health.

Any ideas as to why my teeth have decided to turn its back on me? :(