Gastric Demon or Disease??

To Whom It May Concern;
  
I am a 25 year old female, Caucasian, and for the past five (5) months I have been experiencing a variety of GI symptoms.  I have been seeking help and testing from a gastroenterologist in my local area, and after five months of testing, little progress has been made in terms of solving the problem.  I've tried things on my own to help, but the code hasn't really been cracked just yet.  Mostly, I would just like some kind of feedback as to what I may be dealing with, and perhaps just how long of a diagnostic or treatment road I may be heading down.  I have faith in my doctor's skill and intellect, but they haven't said much so far.  So here's a run down of what's been going on.
For a year before this I've had chronic indigestion that taking 40mg of Pepcid AC and occasional Tylenol Extra Strength relieved.  At the end of March 2008 I had a short bout of constipation that a dose of Philip's helped, and then about 2 weeks later I started experiencing chronic abdominal pain that Pepcid no longer relieved.  I couldn't eat anything without having an awful abdominal pain immediately after, but my bowels were normal.  I could drink Ensure, but not Boost for some reason, which I think started the weight loss.  Throughout the past five months I've gone from my normal 95-98lbs weight down to 78-80lbs (it depends on the day).  My CBC and metabolic panel were normal, upper endoscopy was normal, Giardia test normal (I work in an animal hospital as a veterinary technician).  Nexium and only drinking Ensure and fat free vanilla yogurt for 2 more weeks helped with the pain, and I was able to start eating food again.  I had a 3 weeks bout of diarrhea though which was a little scary, and continued to drop weight.  This eventually resolved on its own and then in a few weeks turned into a month of constipation.  A gastric emptying test showed boarder-line gastroparesis and was given Erythormycin 100mg TID-QID to take before meals.  I take it, but it only helps so much.  From July- August 2008 I had diarrhea.  Scary again because it was constant, uncontrollable, and watery.  Fecal cultures and another test for Giardia came back normal, as well as a blood test for Celiac.  Colonoscopy was normal, though somehow visualization was obscured by stool residue even after a month of diarrhea and 2 days of osmotic prep with liquid diet.  More symptoms have shown up during the months as well ranging from constant bloating and distention (real distention) after eating, abdominal pain and gurgling, obnoxious gas, mucous in stool, random fevers and submandibular gland swelling, and then more constipation now for the past 3 weeks.  My weight still hasn't improved, though fortunately hasn't gone below 77 lbs, and honestly I'd just like to get through a day where I'm not in pain and don't have to fast for about 2 days just to get to that point.  Many of the people around me think that it is somehow stress related, which is of course possible, however I just don't feel that it's all that simple.
I'm sorry this is such a loaded history, but any insights, suggestions, or guidance would be greatly appreciated.  Do I have a demon in my belly, or does it sound like I may have something more serious that I'll have to learn to live with rather than just try to solve or fix?  I'd kind of like for all of this to just be an over extended nightmare that will somehow just go away, but I'm doubting that it will happen all that easily now.
Oh, also, no one in my family has any history of GI disease.  Thank you for your time, and I hope I haven't made this too loaded of question.  

    Sincerely,
      Mary C.