I don't know your full history, and I haven't examined you as your doctors would have, but any time that there is iron deficiency anemia in an adult (especially if you are over 50), I would be concerned about blood loss from somewhere causing it. I would ask your doctors about whether a colonoscopy would a good idea for you, as blood loss from the bowel is one of the more common worrisome causes of such blood loss, depending on your age and the rest of your history and exam. If you are very young, they may not be concerned about this, but I would mention it, and ask if they think colonoscopy would be prudent for you.
In response to your comment above, I am a 31 year old, black female. I have four children ranging from the ages of 6-13. My reason for seeing the doctor originally was because I had no energy. I was gaining weight even though I regulated my diet. Easy tasks were becoming exhaustive and I was having to force myself to move. I was experiencing swelling in my lower extremities, dizziness, and memory and concentration problems. With all of the lab work that was ordered, would low iron cause these problems? And I will speak with my doctor in regards to the colonoscopy.