Not a doctor but my sister had similar symptoms, turned out to be allergic to many foods, have you done food journals yet? It was carrots, anything with carrot in it, barley, etc causing her vomiting episodes. It was regular to when she tried to eat "healthy" each month, because she would consume greens etc, and is allergic to most forms of lettuce. Also reminds me of Chrons/Celiac, hopefully it is something somwhat easily treatable like that, good luck. She went 15 years like that, vomiting regularly until she found out. Good luck!
I sent you a private message with info about my friends support group. Hope it might help!
There are some known conditions (unfortunately by very few doctors) that can cause the problems you're having. A friend of mine has many if not all of the same problems and after 20 years she was recently diagnosed with Nutcracker Syndrome (Left Renal Vein Compression) and SMA Syndrome (Superior Mesenteric Artery Compression) as well as a condition that I have called May-Thurner Syndrome (Left Iliac Vein Compression). Nutcracker Syndrome is a complex, debilitating condition that is known to cause Chronic Fatigue Syndrome as well as many other problems including Hematuria, Dizziness, Fainting, Nausea and Vomiting due to compression of the Splanchnic Vein. It's located in the upper left quadrant of the abdomen which could explain the pain that you're having there.
May-Thurner Syndrome can cause many of the same problems. It's been causing me Chronic Fatigue, Anxiety and Depression for the past 25 years. It wasn't until recently that I got diagnosed and treated for this condition and it's a miracle how much better I feel now. Both of these vein compression syndromes should be checked for as they frequently occur together. A good doctor to go see may be a Vascular Surgeon that is very familiar with these Vascular Vein Compression Syndromes of the Abdomen.
My friend has a support group If you're interested send me a private message and I'll give you her info. She is very knowledgeable about these conditions. The good news is if you have any of these, a simple stenting procedure could give you great relief from you're symptoms, although surgery is sometimes required.