I started treatment for anemia after I went to the doctor. How long will it take for my symptoms to improve?

Weeks. If your anemia was due to an iron deficiency, it will typically take 2-3 weeks for your bone marrow to start producing more red blood cells.
Depends. If your anemia is due to iron deficiency and you have been treated with iron and you are absorbing iron appropriately, your RBC count may begin increasing after about 10 days. Your symptoms may not improve for a few weeks.