It seems from the history that you are having headache on drinking plenty if water. This is very rare to see in clinical practice but few causes like glaucoma
needs to be ruled out.
One of the test done to diagnose glaucoma in the past was water drinking test where after drinkingcwater an increase in intraocular pressure
indicates glaucoma. This can be responsible for headache.
However this is rare to have glaucoma diagnosed by this way but still I advice you to consult your ophthalmologist to rule out glaucoma once.