S.A.
Does he have any other symptoms? Any fever, runny nose, runs??? If he has any other symptoms, I would take him in just in case.
A friend of mine has a 14 month old little girl. Her daughter wasn't eating and drinking very much and was very lethargic. She took her daughter in and they discovered she had RSV. No other symptoms that are associated with it, just not eating or drinking and being tired.
I would take him to the ped because he needs to be well hydrated and if you can't get him to drink much he can become dehydrated quickly. My oldest daughter was a bit sick for awhile when she was five and she started hallucinating. I took her in and she was dehydrated. They had to put in an IV...
Let me tell you she doesn't let herself get dehydrated anymore. She is very good about drinking plenty of fluids now even when she's playing.