It could be gas, your period about to start. I would have pain
on one side
when I would be ovulating. If the pain
is really bad where you can't stand it, you should go see your Dr.
If it's just an annoying pain then I would probably not worry too much about it. It could be just normal aches and pains that everybody tends to get every now and then. If it keeps up for several days or gets worse you should probably be seen by your Dr.
Hope you get to feeling better soon!