If your rabbit is obese, it might be unrinating frequently because of it. You could feed it less food and play with it more so it can lose some weight. It could also be a sign of a urinary infection or other infection.
Rabbits normally do urinate quite a bit. But if the amount seems excessive or unusual for your bunny, be sure to seek the advice of your veterinarian as there may be an illness or renal disorder at hand. Color of urine can also be disconcerting. It can range from light yellow to dark orange-red and still be 'normal'.