Constant burning throat and nausea

Hi, I am wondering if anyone has experienced anything similar to this. I’m 20 years old and have suffered from nausea and burning in my throat for several years now. I have seen two GI doctors who have tried a few different PPIs and have tested me for many things, but I continue to get worse. Currently I am diagnosed with GERD and Fructose Malabsorption. PPIs seem to help with “regular” heartburn which I would get after eating a meal, but the burning in my throat is something different. It comes out of nowhere, usually two or three hours after I have eaten something or when I wake up in the morning. It will last for 2-3 days (sometimes more) straight with severe nausea, bloating, and gas. During these spells I can barely eat anything and medicines like Gaviscon, Zantac, and Pepto don’t even touch it. Then, I will wake up the next day after having a spell and the burning will be gone, but I am left with a queasy/nauseous feeling most of the time. I have drastically changed my diet and don’t eat or drink anything acidic or irritating. I don’t have coffee, chocolate, sauces, fried foods, etc. I also don’t smoke and I am pretty underweight. Does anyone have any ideas or tips? I am so desperate for relief that I am willing to try anything.