Ovarian cysts will exhibit pain in the ovary as well as the back, on coinciding sides. The pain can vary in severity and arise right before, and after, menstrual cycles.
There are a couple of reasons, one is that you are pregnant and what you are feeling is the uterus stretching. Another reason is that you could be ovulating at the moment or are about to get your period. If too strong then it is a medical emergency.
There are two likely reasons, but in any case you should see your doctor. It is possible you have either an ovarian cyst or a mild to moderate kidney infection.
Ovary pain is often associated with cyst on the ovary that are bursting and even ovulation on that side of your body. As most women do not feel ovulation I would lean more towards a cyst.
If this occurs at the same point in every menstrual cycle, it is called mittelschmerz, middle (cycle) pain. If the pain is persistent throughout your cycle, see a doctor.