What Causes Pain In Ear Of A 8 Year Old Child?

My daughter is 8 years old. For over a year sometimes she feels pain in her left ear for 1 min then disappear. Sometime it happens 3 or 4 times a day and normally at school or day time but not happen at night.
I take her to family doctor and specialist, she took her hearing test and so far they said her ear looks normal. My daughter does not drink much water, can this cause problem for her ear? Could you please let me what happen to my daughter's ear? Thank you