Sometimes i feel like i have to throw up after i pee. why?

Good question.: I think the answer may be something simple like a vaso-vagal reaction, where your blood pressure drops suddenly after such things as urination, passing a bowel movement, or sometimes even a coughing spell. Other symptoms are usually blurred or altered vision and lightheadedness. If this sounds familiar that may be your answer, but it still is probably best to discuss with your doctor in person.