Since you havnt drank water a lot and suddenly started your body isnt used to that amount of pure fluid that the stomach does not have to digest other substances, such as sugars, carlories, carbs and sodium. Thus is runs through you faster. The water fills up your bladder and makes your go pee more. Your body will adjust to the amount of water and your bladder should get a little bigger in time. But you should also see if you have a Urineary Tract Infection. If it is sometimes a burning feeling when you pee, that could also be a sign. I wouldnt worry just yet if your peeing a lot. If other signs arise, then go see a Dr.