For the last 3 months I have had my period every 19 to 21 days and it has lasted for around 6 days. I always get painful cramps, lots of headaches and feel quite ill. My period is extremely heavy, and I'm a bit worried. Is this normal? What does it mean?

Well not everyone is the same. Most menstral cycles are every 28 days but that doesn't mean that yours have to be. Your hormonal flow might just be a little higher than average. If the pains become more severe and start to affect you I´d suggest you'd see a doctor concerning them. Other than that you should be fine :)