Fitness Instructor Having Pain Under Ribs Close To Abdomen. Cause?

I am a female, 51 y. old, active fitness instructor, no health problem, 3 kids. I teach 10-11 hours of fitness per week. For more than 6 years now, I have been having this pain under my last right ribs, close to my abdomen, that no doctor could explain. No nausea, no fever, no shortness of breath, no past accident,... like a side ache after a fast run...just this pain that makes me feel like resting in a half seated position forever. The pain vanishes for long period of times, then comes back to interfere with my movement and energy, and stays for days.
I know the symptoms are vague but if you have any idea of what might cause it...