Louise, headaches are part of the detox - they usually don't last longer than 3 or 4 days (but can last as long as 5). 3 weeks is unusually long. Among your supplements are you taking potassium? It's usually the culprit when headaches are concerned. The Eades, of Protein Power, suggest 400mg of potassium while actively losing - and then again when exercising intensely, or on days when it's very hot. Are you taking 400mg? Upping your current dose might do the trick. If you're drinking a lot of water (in excess of 4 litres) I'd think this would be the problem.

Nat