I was diagnosis with an iron def. anemia 4 weeks ago (cause not yet known) and had 1 dose of infed, iv. but am still tired.how long to take effect?

Not yet.: In my experience it may take up to 4 weeks for intravenous iron to have an effect on the hemoglobin. However, this will not change your tiredness as it is associated with both low hemoglobin and the absence of iron. You need to replace the iron until the reserves are full otherwise the anemia and your symptoms will persist. If this has been done look for other causes of the fatigue.

See below: If your hemoglobin is above 10 gm, then anemia is not the cause of weakness. It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. It would be prudent to see your doctor and discuss if you may be depressed. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking.