I think the first thing to do if you notice this problem is to see a doctor! I know stool samples people do at home check for "occult" or hidden blood, so I can't imagine why someone having these symptoms for any period of time wouldn't want to see a medical professional.
Go ahead and change your diet for a few days. Eat high fiber, or go on a soft foods diet, or a bland or "white" diet for a couple of days and see if the problem resolves. If it does, you can probably wait until your next check-up, but if you keep seeing this problem, it's time to make an appointment.