Could this be a sphincter of oddi dysfunction?

A couple of years ago I went out with some friends for St. Patrick's day.  After having a couple of drinks and standing around for a couple of hours, I started to get a severe pain in my epigastric region.  I ignored it as long as I could, however, I started to double over in pain and needed to sit down before I passed out.  After sitting for about 20 minutes, I was feeling better, so we got up to mingle.  After only 10 minutes, the pain returned and I need to sit down for the rest of the time we were out.  The pain, in total, lasted about 5 hours.

Since this first time, I have had 5 "episodes".  One time was so severe, I was curled up in the fetal position for almost 8 hours.  The pain only went away after I finally got nauseous enough to throw up.  The last episode was just over a year ago at a friend's wedding where after having a good meal and drinks, I started to feel sick and could only sit down (I ended up leaving early because I was in enough pain and I was missing all the fun!).  Each time the episodes occur, it is in the epigastric region and is a sharp, tight pain that lasts for at least 4 hours.  It seems to be set off after I have too much fatty/greasy foods or have too much to eat/drink.  Standing really seems to kick them off.  

I am extremely careful not too eat too much fatty/greasy food, or too much food/drinks in general, especially if I know I will be standing around.  I have become scared to go to get-togethers or out with friends out of fear that I won't have a place to sit down.  If I start to feel my stomach/epigastric area start to tighten at all, I stop eating/drinking and sit down immediately.

I did see a doctor about this problem about a year and a half ago and was sent for an ultrasound on my gallbladder to look for gallstones (there were none).

Any thoughts on what this could be?  Could this be a sphincter of oddi dysfunction or something else?