Could drinking almost 3 litres in the morning cause headaches.i am on lexapro (escitalopram) for 12 months and i was blaming them. thanks?

Depends: what are you drinking? why 3 liters? IIf someone else asked you if that might cause a headache, what would you tell them? If you meant alcohol it seems like some guidance is really called for. Time to ask the dr who's prescribing the lexapro (escitalopram). If you meant water, that's still a lot and you might share that - but your dr cant help in an information vacuum.