Side pain even when not running

I am a nearly fifteen year old girl and for about 10 years I have been occassionally getting an ache in my left side, always in the same spot. I usually get these aches when I have an important race or athletics carnival (I’m a runner) and have a big workload. The pain will come early in the day and last until the next morning (it goes away during my sleep), gradually getting worse and worse until I can’t stand up anymore and have to lie down. Usually I don’t notice the pain when I am running but all the time in between it hurts. Any help or advice would really be appreciated. Could it be some type of growing pain?