As it gets better on lying down, first possibility is you are having postural headache
as you are not taking proper amount of liquids. try to take at least 2-3 liters of water every day. you should be able to pass 3-4 times clear urine per day. Also iron deficiency
is a possibility if you are having heavy periods
and poor diet quality lacking iron. Better to get hemoglobin levels checked. Low blood sugar
can be easily ruled out by checking sugar using glucometer. Try to take proper diet, nothing to worry.