diabetes and thyroid problems ruled out! now what?

I have been urinating excessively for the past 6 weeks.I've had diabetes and thyroid problems ruled out.My urine sample proved free of infections.Still,I need to urinate no less than every 30 min.Water goes straight through me,and I often feel the urge to urinate again after I relieve myself.

Up until about 4 hours before bed,the urine comes out without effort.After that time period,it becomes more difficult to urinate, while the urge is still strong.I also feel that I don't drain all urine completely,and the stream does not exit uninterrupted.There has been no blood.The urine is generally not dark.I feel no pain when I'm in the process of urinating.However,I've found that when I lay on my left-side the urge is much stronger.Standing upright seems to alleviate the urge.I also have a discomfort on my left-side,parallel to my groin.

What problems could I be having?Is dehydration a concern if water is going right through me?Should I drink more water,even if I drink plenty to begin with?