Why do i wet the bed? im 17!?

For the past 6 months i have wet the bed non stop. IV tried not drinking nothing before i go to sleep but it still occurs. IV found that if i fall asleep sitting down like in a recliner or a chairi wont wet my self.but as soon as i fall asleep on my mattress i wake up wet the next morning. I don't really drink water. Could that be the problem. Please help....