What Could Be Causing An Uncomfortable Pressure-feels Like I Need

What could be causing an uncomfortable pressure-feels like I need to urinate but when I go its hardly anything. Then, I lay down and I have that feeling again in 5 minutes. This goes on constantly and I am unable to fall asleep. It is the same pressure to urinate whether I have drank a lot of water or nothing--feels the same. I am not diabetic or overweight. Could caffeine intake be causing this condition or something else. It is really interfering with my falling asleep at night.