DD (6, only child) complains all the time about being tired BUT doesn't seem to get too tired to climb the stairs etc.
She does seem to tire out more easily than her friends sometimes.
Mind you, she's complained about being tired like this since she was 3!
We took her to the doctor then and they ran blood tests and said she was fine. The complaining eventually went away, but now it's been back for a few months.
She eats and drinks normally and gets enough sleep.
I just don't know if it's time to take her back to the doctor again...