You should go see your doctor
and discuss any symptoms or concerns in detail.
Ferritin is a blood test physicians use to measure how much iron stores we have in our body. A low ferritin is a sign of decreased levels of iron in your body. It can affect your breathing by making your serum iron levels low. Serum iron is needed by the body in order to make hemoglobin and effective red blood cells, which carry oxygen from your lungs into your body. If you have low ferritin levels, which are leading to low iron levels, your hemoglobin and red blood cells are also likely to be low. This means that your heart and lungs have to work harder in order to deliver oxygen to your tissues, especially when you exercise or exert yourself. This could explain why you feel short of breath.
You should consult with your physician about doing additional testing to discern the cause of your iron and ferritin deficiency and, if appropriate, start replacement with iron therapy. It will take some time for your iron stores to replete and your blood counts to rise if iron deficiency is the cause. Please have an in depth discussion with your doctor about how to address your symptoms and if you need any additional testing.