Keto won't help with your obesity, most likely. A permanent change in diet would be better. Keto might work for a short period of time, but you need permanent change that will last. You also need to exercise. But before you do anything you probably need to talk to a doctor. What you describe does sound like it could be an ulcer, but it could also not be. Nexium doesn't treat ulcers, it treats heartburn. Taking it regularly will cause your digestive system to respond to the acid suppression by making more, as it must have it to digest protein and some minerals. It's a short-term treatment for a short-term problem. Ulcers today are believed to be caused by a bacteria called H pylori, though probably not in all cases, and by taking certain meds such as the ibuprofen you were talking about. But there are other digestive problems that feel like an ulcer but aren't. You can get tests from a gastroenterologist where they will look inside you for inflammation or for H pylori, and if you have it they treat it with antibiotics, not Nexium. But if you're morbidly obese, you probably don't eat very well, and so it could just as well be that catching up to you. The other thing it could be is a sleep disorder, such as apnea, which affects the obese most often. When you eat, a lot of digestive problems caused by things such as reflux and ulcers feel better because your digestive juices have actual food to work on rather than working on you. But as you sleep they can, when your digestive system goes awry, go up instead of out and cause problems, especially if you lay down soon after eating. I got a chronic stomach problem as well from being told to take ibuprofen for too long for pain, and I'm not obese, so it's a common problem with docs prescribing meds without knowing a whole lot about either you or how they affect people long-term. You kind of have to do your own homework to make sure your doctors aren't killing you once you get a diagnosis to make sure the treatment is the right one. But again, you're not going to be able to self-diagnose. It seems clear your weight is starting to catch up to you, but just how isn't clear, so I'd suggest seeing the right docs and find out if something is going on, but whatever you do, you're either going to get to work on the weight by living a healthier life or stuff can happen as you get older. All the best.
I'm glad you went to the urgent care! I know that shortness of breath can happen during gerd because the stomach acid can creep up and enter your lungs. You are most prone to this during sleep. Here's an entire very easy to read article on it. https://www.healthline.com/health/gerd/shortness-of-breath Let me know after looking at it if it sounds at all familiar to you.