Drinking so much water but still thirsty..do I have a problem?

I drink at least a gallon of water every day, but I seem to constantly be thirsty. I don't drink anything else, and I rarely use salt. (Only if I really crave it) Is this normal, something I should worry about, or am I doing something wrong?

Answer:
No, this does not sound normal. Dr. Rosedale said, you should get a urinalysis (common lab test of urine) and also get your blood sugar checked..