My 8 Year Old Daughter Complains Of Her Legs Hurting.

My 8 year old daughter complains of her legs hurting. Mostly at night but some during the day as well. She tells me her legs are shaky and "give out" during the day several times. We use a heat pad, tylenol and leg rubs every night before bed. This has been going on for several years, but she has just recently been able to explain to me that her legs give out and are shaky. Is this something that I should be worried about. Our family dr. has always said she just has growing pains. thank you