9 week old male chihuahua not eating much not drinking much either but seems to be in good health sleeps a lot but still likes to play.

We get his food dish amply supplied with same food the breeder fed with.
Tom Coley >Removed<

If I were you, I'd take the pup to the vet. Puppies are typically not lethargic and have huge appetites.

When did you get the puppy?

If its recent, the pup could be a bit stressed after leaving the litter. Eating and staying awake longer will follow once the puppy feels more comfortable in his new home.

Dogs have a wonderful way of hiding their pain, discomfort and other ailments. Typically by the time you notice something is not right, the dog is in advanced stages of either pain, discomfort, etc.

Just to be sure, take the pup to the vet or contact the breeder and ask if this is normal. If he is a good breeder, he will help you through this and give you better advise about his own dogs than anyone else on here, or even a vet office can.

If she's OK after a sleep, then I think it's no problem. Probably because chihuahua breed is small, they don't eat much..