Blood test showed anaemia but heavy periods have been controlled (noriday) and i eat a lot of iron rich foods, so how can i be anaemic?

Timing is everything: It takes 90 days to initiate red blood cell production and the red cell life is only 120 days. Thus, you are constantly losing red cells normally, while you are still in the manufacturing process. if the anemia was very severe, it could take up to 6 months to restore normal values IF you are using iron Rx and not just eating iron rich foods.

You lose more blood : You lose about 1% of your blood each day by the normal lifespan of the red blood cell being only approximately 100 days. if you lose so much blood in your body cannot produce blood faster than you're losing it you will become anemic. In addition if you are are deficient your body is unable to respond quickly enough in many cases to produce blood