Those are normal I think, I asked the diabetes nurse once what normal readings would be for blood sugar in someone without diabetes, and she said a bit over 4 or so. So in answer to you question, what would cause this to happen? Not having diabetes is what. The recommended blood sugar ranges for diabetics are so much higher than normal are to prevent people dying of hypoglycaemia, I think the mechanisms for raising blood sugar don't work properly or something.
How many litres are you drinking a day, don't think urine should smell much if you drink enough, mention your symptoms to your GP that's what they are there for.