How can I stop stomach pain due to invisalign?

Right after using invisalign, I started to feel a strong burning and pain in my stomach, right in the middle in between the ribs, a little nauseous, not diarrea. I am healthhy and no stomach issues. I noticed a lot of saliva production, like when chewing gum but worst. I imagine having something in your mouth and not receiving food - the body produces saliva for digestion but you eat nothing. I wished I knew this before buying invisalign $$$. Is it possible ? How can I stop it ?

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