The general rule of thumb is that if the pain is severe (prohibits you from doing daily activities), call your doctor/go to the ER (preferably both) right away.

Kidney stones often presents more as flank or back pain at first although the pain may radiate(move) to other areas.  Appendicitis is again more lower right abdominal pain although again, this cant be ruled out either.  If it is pleuritis, then usually when you breathe/inspire, the pain often intensifies. 

If you do have upper right abdominal pain, gallstones, gastritis, and ulcers are the prime sources in a number of patients.  Notice carefully if eating meals or taking antacids of any kind improves or worsens your symptoms. 

A simple test to see if the pain is external (musculoskeletal such as costochondritis or a broken rib) or internal (gallbladder, stomach, kidney, etc) is simply press on the area where the pain seems to be localized.  If it gets significantly worse, it suggests a superficial cause (broken rib, strained muscle, etc). Although this method is not as reliable, it at least helps your doctor to notice the rough location of your pain and could facilitate diagnosis.

At this point, anything could be the cause (even the heart)..so first:

1. See a physician immediately
2. Note carefully your symptoms including: duration, severity, location, things that make it better or worse, and finally associated symptoms (nauseu, vomiting, breathlessness, etc.)
3. Note all meds and past medical/surgical conditions of which you may have or have had in the past

Hope this helps...