Blood Test Results Shows I Now Have Low Iron Count.

Blood test results shows I now have low iron count. been on iron supplement for 6 weeks with no change in level. Just finished having complete virtual colon test (waiting for result) I have been on aspirin for at least 20 years. Have been on higher dose for a while also. Could this have done damage to my stomach that would cause bleeding. My chest was check and that is ok. The doctor feels that a must be bleeding somewhere to have this low iron count.
What are your thoughts