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Pain responding to PPI omeprazole
was most likely due to anygastritis or acidity.
And its a burning pain mainly in epi gastric region. But as your pain has recurred and it is not responding to ppi and it's dull aching type, then most likely it's due to some other cause.
Visit a good doctor and get endoscopy
done to rule out any pathology. If no lesion found then most likely some there's nothing abnormal.