HELP!

My brother has been feeling nauseas for a month+ now. He is 12 years old and he gets this sick feeling after he eats or sometimes when he wakes up. We have tested for coeliac disease (gluten intolerance) and negative. We have put him on lactose free milk and he still felt nauseas. He has only vomited once so far and i have looked at everything on the internet. He has been to the doctors, had stool tests and the doctor said they saw a bit of bacteria but might not be the cause of it! What could this be?! Is there any medications that will fix it and stop for good and nothing drastic like surgeries! Any information will be good at this time, we just need to figure this out. The only thing i can think of now is cancer. PLEASE HELP ME AND MY FAMILY!