I am worried! My doctor's office called to tell me that my red blood cell count is low and concerns them. They say they will call back later today but in the meantime, what can this mean? Leukemia? Anemia? Any clues? Please let me hear from you if you have had a similar experience. Thank you.

The most common reason for low RBC count is anemia. There are many people who have mild anemia. I would not get too concerned just yet.

Welcome on board! Sorry you have this problem...
Just want to share it with you - who knows if it may help
My husband got a bad result regarding his low platelets. His Doc sent him to hematologist/oncologist and he was checked for lukemia, and all possible blood desorder. We are so lucky that our doctor very good and persistant.
He took my husband's bone marrow and sent it to CA (the only 2 places in US to check if person has rare condition called Govshei's disease). It came back positive. No treatment for this (you born without one chromosome, he never knew about it until 51 years old) and your symptoms are : low blood platelets, or spleen inlarged, pain in a legs, being tired all the time.
You can be a carrier or diseased. You may have symptoms or not, or you can have one symptom only - but it is always comes from a parent or both.
good luck to you