My 5 year old has had diarrhea since late monday. It has gotten better but it has been too long. Do I need to take him to a doc. On monday he had a small fever, that passed.

Usually. Usually stomach flu (gastroenteritis) which commonly causes diarrhea lasts about a week or so and should definitely decrease as the days go on. If your son still has diarrhea and/or has blood, mucous, or parasites in the stool then he should be seen by a medical professional. Not only will a work up of diarrhea be done, but also an assesment of his hydration. When diarrhea goes on for a while one can become pretty dehydrated and often times require IV hydration. Make sure he is drinking plenty of fluids and pedialyte. I hope he is better soon.