do you suffer from migraines, maybe its that.
my sister went through a stage of suffering from headacehs and stomach pains and it turned out to be from her diet (although the dr did say that it wasnt definite but was the most likely cause). she ate chocolate and biscuits and sweets all the time, but my mum has to like force feed her vegetables. but my parents got her to change her diet, and they stopped.
if it carries on go and see your dr, it could just be stress or tiredness.