Whenever i lay down after i drink some water (any amount), my lower back (possibly around my kidneys) begins to hurt. it's just very uncomfortable.

Drink water: There is no way that water drinking can be involved in back pain. A hiatal hernia hurts under the rib cage. Sx are from you spine or rarely Renal. Check w/ Murphy punch striking kidney area with the pinky side of your fist. A light tap is painful with kidney problems. Otherwise get a thoracolumbar x-ray for old injury or congenital problems. IV shooters get a disc infection.