Welcome to the gastroenterology community! You can have idiopathic gastritis meaning that no cause is known. Omeprazole is most likely not causing this. I would recommend talking to your gastroenterologist about this.
I am just 15 years old and have suffored with abdominal pains for over a year now. Finally I have been referred and diagnosed with possible Gastritis. Despite my H-Pylori test being negative, my paediatrician told me that it was still a possibility. After taking the given medications (Omeporazole, and 2 antibiotics) I still find no relief from my symptoms. I am underage and ultimately do not drink, although stress from GCSE exams is a possible symptom. I have a sick/bloated feeling in my upper abdomen, causing me to feel the need to burp/be sick but am able to find no relief. My next hope is having a camera down to see what the real problem is. Any advice?