It's a good idea to have your ferritin checked regularly.
And Marathon5, you should also know that long distance running may also be a partial cause of the low iron.
http://www.pathologystudent.com/?p=2290
Aside from the running and the possibility of a "slow leak" causing your low iron, it is also possible that you are not properly absorbing the iron you are eating or taking orally. My own personal experience was that I was chronically anemic until I adopted a gluten-free diet.