R.M.
It sounds to me like he is dehydrated,,,you need to push the fluids....water...pedialyte...gator ade. You just need to get the fluids in him. As long as he is doing alright..not complaining of stomach ache, isn't sweating having muscle cramps etc...you should be able to wait until tomorrow morning.
Here is a website with some of the signs of dehydration...and suggestions as to when it is necessary to seek medical help.
http://www.symptomsofdehydration.com/