I had severe left upper quadrant pain, happened suddenly, radiated to left shoulder, am 26 no past medical history. what is the cause for that pain.

LUQ pain: Your abdominal pain could be a number of reasons. Would need additional symptoms/descriptions to assist ruling out possible causes. Make sure you are not constipated, which can present with those symptoms. Take citrucel as a trial with adequate hydration. If symptoms persist, suggest abdominal ct and being evaluated by a local physician.