Diarrhea during exercise

Patient: Hi, i’m a 21 female from canada. i’ve noticed in the last month that every time i walk more then a mile, i feel nauseous and i end up having diarrhea. this has never happened to me before; ive been walking a mile or two every few days for the past few years. and i also get this feeling when i am aroused. the sickness during arousal has been happening on and off for about 5 years now. do u think it could be anything serious?by the way, i did have an operation on my urinary track (apparently the tube to my bladder was too small and they had to enlarge it) when i was 5 years old. i dont know if it has anything to do with my current problems, but i thought id mention it anyways…

Doctor: