goodtoknow says: If you're feeling exhausted and washed out you could have anaemia. It's a common problem with your blood where you have less red blood cells or haemoglobin than normal. It's the red blood cells that carry the oxygen around your bloodstream. You'll feel tired and may be pale because your body's getting less oxygen. Anaemia is often diet related, you may not be eating enough iron, essential for healthy blood. If you have heavy periods or are pregnant you're more likely to get anaemia too. Iron tablets should bring your levels back up again.
For a full medical explanation of the causes, symptoms and treatments of anaemia from patient.co.uk, read on.
This leaflet provides a general overview of anaemia. There is a separate leaflet on: Anaemia due to lack of vitamin B12.