I do not buy the metabolite argument, but I agree with most everything else that has been posted. Exercise will increse metabolism and the concentration of the metaolic wasts products (primarily creatinine and urea, but also ketones if your carbohydrate intake is not keeping up with your energy expendature) in the urine, but the volume of urine you produce should not increase. The metabolic waste from using carbohydrate as the energy source is carbon dioxide and water. The amount of water is small compared to the water lost through sweating, though, and carbon dioxide is eliminated via the lungs, not the kidney; thus, increased production of metabolic waste products, even though real, is not likely to increase the volume of urine.
Do you have edema ("oedema" for English speakers outside of the US) when you are not exercising? If so, the increase in circulation during exercise could remove the extra fluid from the tissues and return it to the blood stream, which would result in an increased volume of urine. If this were the case, though, I would expect that any aerobic exercise would cause an increase in urine volume. In fact, sitting with your feet elevated while watching television would cause an increase in urine volume.
Drinking more than you are sweating is the most likely cause. Even though your recent lab work was normal, there is an outside chance that you are in very early type II diabetes. In early stages of type II diabetes, the fasting glucose is normal, but glucose goes up immediately after eating. There could be enough sugar in the Gatorade to cause plasma glucose to go above 160 mg/dL, in which case, the kidney will spill glucose into the urine, and the osmotic effect of the glucose will pull water with it. If you had a normal hemaglobin A1c (although most physicians do not measure that unless the glucose is abnormal) or a normal glucose tolerance test (again, not usually performed unless diabetes is highly suspected), glucose in the urine is not going to be the cause. Diabetes is a longshot, but possible.
How much do you drink while you are exercising? Have you weighed yourself before and after you exercise? If you weigh more after exercising than you did when you started you are drinking too much, and that is why you need to go so often.
