Doubtful that it is a stricture this far out from WLS. You need to see an experienced gastroenterologist to get a proper diagnosis. They may perform a variety of tests, such as EGD endoscopy, upper GI, Bravo pH, manometry, etc.
GERD/heartburn/reflux is a known risk of VSG and it can occur even in people who didn’t have it pre-op. This is one of the main reasons people have revision surgery from VSG to RNY, to resolve or improve GERD/heartburn/reflux.
VSG is contraindicated in people with pre-existing GERD. Because of my history of GERD prior to bariatric surgery, my surgeon would only perform gastric bypass on me, not sleeve gastrectomy.