According to the internet:
Nausea and vomiting are the most common complaints after bariatric surgery, and they are typically associated with inappropriate diet and noncompliance with a gastroplasty diet (ie, eat undisturbed, chew meticulously, never drink with meals, and wait 2 hours before drinking after solid food is consumed). If these symptoms are associated with epigastric pain, significant dehydration, or not explained by dietary indiscretions, an alternative diagnosis must be explored. One of the most common complications causing nausea and vomiting in gastric bypass patients is anastomotic ulcers, with and without stomal stenosis. Ulceration or stenosis at the gastrojejunostomy of the gastric bypass has a reported incidence of 3% to 20%. Although no unifying explanation for the etiology of anastomotic ulcers exists, most experts agree that the pathogenesis is likely multifactorial. These ulcers are thought to be due to a combination of preserved acid secretion in the pouch, tension from the Roux limb, ischemia from the operation, nonsteroidal anti-inflammatory drug (NSAID) use, and perhaps Helicobacter pylori infection. Evidence suggests that little acid is secreted in the gastric bypass pouch; however, staple line dehiscence may lead to excessive acid bathing of the anastomosis. Treatment for both marginal ulcers and stomal ulcers should include avoidance of NSAIDs, antisecretory therapy with proton-pump inhibitors, and/or sucralfate. In addition, H pylori infection should be identified and treated, if present.
After my surgery, my surgeon put me on Omeprazole [Prilosec OTC) which is a proton pump inhibitor for the first year to help my stomach heal properly. I did not experience recurring bouts of nausea. After the first year, I discontinues and all was well.
So if you are not taking any NSAIDs such as aspirin and if you do not have an H pylori infection, then perhaps you have an ulcer.