Hi,Symptoms you are describing are symptoms of extreme sensitivity to" CLASS 11 "fungicide widely used on vinifera grapes/Please do some research on the subject.
If the doctors thought it was a brain tumor, they would have given you some imaging studies asap. Passing out can be autonomic (blood pressure not coming up fast enough when you stand), ear issues, neurological - so it may take a few tests. Your doc can't offer anything as the explanations are pretty endless at this point with a tumor being a pretty rare one especially if that is your only symptom.
I would wait until you see a doctor, get some more testing - but having normal studies at this point should make you feel better.