I have anaemia and have been taking some iron pills from last 3 months but these days i feel very tired, always sleepy and sometimes even dizzy. why?

Need to examine: It is not feasible to provide a meaningful answer without taking addition history, a physical examination and some tests. It would be prudent to see your doctor.

Different Issues:: Anemia is ↓ed concentration of red blood cells. Iron deficiency (a result of blood loss; iron cannot be recycled from cells which have left the body) is only one of many both common & rare reasons for anemia. Iron deficiency & anemia: 2 different issues; taking iron is no guarantee of resolving anemia. Similarly, fatigue/dizziness common result of many issues; rarely due to anemia or anemia alone.