L.D.
You should call your child's pediatrician, if you haven't already and get recommendations from him/her - Your son may need to be seen in person. A symptom of dehydration IS decreased urine output. If he has no urine output, no tears, & dry mucous membranes then your son will need IV hydration.
You should always feel comfortable calling your pediatrician with questions/concerns like these. If you don't feel comfortable with your pediatrician, then you need to switch peds.