don't put too much stock in my (or anyone's) post. anemia can be very serious, so stick with the dr's advice.
that said, it's not uncommon for endurance athletes to test 'anemic'.
I use the quotes because the measures you mention are simply concentrations. And one early, and robust, response to endurance training is an increase in plasma volume. So, if you have the same number of red blood cells as before (whenever that may be), but more plasma (essentially water), then your concentrations are down. although you may have a perfectly healthy total number of red cells. In this case, it's unlikely that your performance would be effected.
What to do? Keep training and don't worry about it (as long as the bill of health is good - refer back to the first line as necessary).
Not a bad idea to look into the symptoms of anemia to see how they stack up to your case. But remember, fatigue is not "I rode 200 miles this week, and I'm tired", it's "man, I just walked up the stairs and I'm exhausted".
In any case, the colonoscopy is probably a good idea, both to rule out a bleed, and to screen for cancer.
So, I guess my advice is to be careful about it, but don't take it too serious. But also remember it could be serious. (this is why you don't listen to the internets)