Persistent vomiting and inflamed stomach - please help

My husband has a history of gastrointestinal issues. He has been diagnosed in the past with a stomach ulcer, a hernia, once had a fistula, and most recently, has been dealing with diverticulitis. However, a new issue has cropped up that perplexes me a great deal.

For the past two months, he's been dealing with intermittent bouts of vomiting. The first time, he was diagnosed with the flu, and put on Tamiflu, and things got better. Then about a month later, he was out sick again because of nausea and vomiting. Then it went away. Over the past week, it's been a problem yet again. Here's the recap:

He began vomiting on Monday morning, stayed home from work, and called his doctor, who ordered a CT scan because the stomach area where his diverticulosis is present (lower left abdomen) was tender. The CT scan showed no inflammation, but did reveal a kidney stone that hadn't yet dropped. Bloodwork was tested and came back normal. He then made an appointment with a gastroenterologist. Wednesday morning, he was throwing up again, and went to see the GI doc that afternoon. She agreed that his symptoms did not correlate with diverticulitis, and ordered an upper endoscopy and a blood test for Celiac disease. Friday morning, he began vomiting again, this time severely enough to require care in the ER. They stopped the vomiting with anti-nausea medication, gave him some fluids, ran the same blood tests as earlier in the week including a panel for the pancreas (which all came back normal) and sent him home. He was fine all weekend.

This past Monday morning, the vomiting returned. He called and got in that day for this endoscopy. The endoscopy revealed a red stomach lining. They biopsied to check for Crohn's, Celiac, H. pylori, etc. We expect the results early next week. He vomited twice again this morning, but seems to be OK now.

What on God's green earth is causing this? We are frustrated and perplexed. He is stressed out because if all the work he's had to miss, and just wants to know what is going on. Does anyone have any ideas? Thanks so much in advance for your guidance!