Possible Water Retention?

I was banded on December 28th. After five days of straight water I am up to 3 shakes a day and 64 oz of water. I am to drink one ounce every five minutes. With all that liquid that I take in, is it unusual for me not to be eliminating great amounts of urine? On a regular day without lap band surgery and not dieting, I would be going to the bathroom much more often. I have lost weight but not anything one would think on such a drastic diet like this. I mentioned it to the doctor and was asked what color my urine was and as long as it is not really dark, I am not retaining water. Has anyone else experienced anything like this? Looking forward to your input. Thanks.