Had the same problem myself in USAF training. I had flown as a pax for years without a problem, and thought nothing of it. However, on my first USAF traininng flight I was sick. Very sick. Next flight, a little ripe. All flights after that, pretty much no problem at all. To echo 27mm, keep at it. I haven't been sick on an aircraft for probably 25 or 30 years now.