Yeah - I'm currently on WeightWatchers but I haven't been eating my bonus points. Maybe I should be eating a light snack before running (i.e. banana, snack bar).
Yesterday I had an apple and drank 1.5 litres of water before going for my third run, I also had a sports drink during and after running, and I didn't get a headache.
Thank you everyone - you've given me lots to think about. And, by the way, went running last night, and enjoyed it more than ever.