well, I don't have that problem, but you may have a metabolism that doesn't like missing a meal. If possible try to carry a marsbar (lots of sugar aka engery in that) around with you in winter and eat that if you start feeling weak or uh... something similar that won't melt in summer I guess. I'm not sure though why you would feel like this, it may be worth getting it checked with a doctor. Maybe your diet doesn't include enough carbs or something, or your body is not very good at storing/releasing the carbs ??? I think it's worth checking with a doctor just to be sure...