What Causes Constant Urge To Urinate?

My 16 year old daughter feels like she needs to urinate but she may have just gone pee. There is NO pain. She is not more thirsty but her stress has increased. It has been 4 days. The feeling like she is peeing or is about to pee her pants but she doesn't. It feels exactly the same even right after she urinates. She does drink 4-6 cups of coffee a day. Now she doesn't want to go to school because she has to go out to the toilet even though she doesn't pee. Again. She has no pain. Pls help we booked Dr appointment but it's next week and she has exams!