Whats causing this pain in my right side?

Ive been getting unbearable pain in my right side just under my ribs. Ive had an ultrasound scan on the whole of my abdomen including my kidneys, liver, spleen, gall bladder and stomach and it has all shown up clear. So what is my pain, it comes on really bad when i eat which is why the doc thought it was something to do with my stomach like an ulcer etc but its on the wrong side! My pain is on my right side and our stomach's are on the left!! I did wonder about my oesophagus but it seems a bit to low down for this also. Its really starting to get me down now. What could it be, any ideas??