One thing that happens when using these PPI medications is that the stomach notices that there is less acid production, so it starts trying to make up for it and will make even more acid. This is one of the reasons why these medications should only be used short-term. You can find this information on mercola.com. He also has suggestions that can help with these upper GI issues.
About 4 years ago I suddenly got acid reflux problems and had all kinds of tests and nothing showed up. I developed inflammation of the gall bladder shortly after developing severe acid reflux and had to have it removed. This didn't solve my abdominal pain I was having. My symptoms continued to get worse. I developed fibromyalgia for unexplained reasons, elevated rheumatoid factor along with night sweats, headaches, migraines, fatigue and more. I was recently diagnosed with lyme disease. I am currently being treated for bartonella infection. This causes stomache pain, fibromyalgia, digestion problems, fatigue, rashes, restless sleep, swollen glands and more. Bartonella can be contracted many different ways, through cat scratches ( cat scratch fever), fleas and ticks. It is one of the most common infections in the world and rarely treated in the US. Doctors do not look for this condition. It is worth looking into.
I'm assuming that you had a gastroscopy done?? Did they say anything about having gastritis?? Gastritis can cause stomach pain/burning due to the stomach lining being inflamed. How about ulcers, did they say anything about an ulcer??
How long have you been on the Prilosec (Omeprazole)?? Also how long has it been since you have had the gastroscope done??
Sorry for the questions, I just would like a little more info so I can try to help you. :)