Unfortunately abdominal pain and vomiting are very general symtpoms that can be caused by so many different reasons.
It is real 'stomach' pain = location in stomach
or 'stomach' pain as in abdominal pain? If abdominal pain, which quadrant?
When routine stool (for pathogen bac and parasites), blood tests (liver, pancreas, electrolytes, thyroid hormons, pancreas, red blood, white blood count, CRP, celiac antibodies, glucose ....) revealed nothing (were negative),
other tests (from different blood tests, breath tests for H.pylori to malabsorbtions) to ultrasound, other scans, scopes can be done to at least exclude xyz.
Exclusion is already some peace of mind, but of course not helpful in reducing the pain.
Docs will check through a list of possibilities, starting with the most obvious or dangerous.
From there it needs observation and patience and ideas, what else could be done.
We have no idea here in this forum, what tests were already performed so others could give you an idea, what they had done additionally with similar symptoms.
Sometimes it is something rare like autoimmune disease that affects GI, 'gastroparesis' often a cause for vomiting (gastric emptying slow, as to why is a different issue. Often not found),
often the cause is not in the intestine actually, it can be a certain kind of porphyria (urine test), or something like MbAddison (low cortison, easy: 24h urine test).
Best of luck!!!
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Hope you find some symtpom relief since that is important, too.