My 17 Year Old Daughter Has Always Had A Sensative

My 17 year old daughter has always had a sensative stomach but now about once a month or so she will actually throw up as in stomach gurggles, she's nauseous, throws up then feels better. We thought it was period related because a couple times it was the day before but other times it's not. She's very athletic so she is not overweight at all. She's not on any medication but I took her to a gynecologist because we thought that was the cause. Now we are confused.