Prolonged nausea?

Ok so everyday when I'm at school in the morning my stomach gets really nauseated and then by me third class, it goes away. I went to the doctor and he said it might be because of anxiety or stress but I'm neither of those. I'm starting to get worried about it and I want my stomach to return back to normal. Anyone have any clue what it is or how to help out?
Prolonged nausea?
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