I don't know if you've ever gotten motion sick, but I disagree. I've had a flight instructor tell me that motion sickness was a psychological problem and if I keep on thinking about getting sick, I WILL get sick. I guess all that stuff about the inner ear was nonsense to him. Probably if you were stressed out, the motion sickness might WORSEN, but I don't think stress itself will cause that. I never actually worried about getting sick - it was something that just happened if conditions were ripe. For me those conditions were 1) empty stomach, like others mentioned. This was almost always the factor. 2) once in a while when it's turbulent. When I was an instrument student one day we were flying in IMC, down in Florida where it was super hot and bumpy, I turned around in my seat to grab a chart from my flight case... and as soon as I whipped my head around the nausea hit me like a ton of bricks. You know what my instructor (who had apparently never gotten motion sick) recommended me to do? "Read something, you'll feel better."
I think you'll get better you autopilotfrank, and if you feel motion sick once in a while even now after flying for however many years, I think that is completely normal.
What helped me not to throw up once the motion sickness already hit (and there were a few times during training when I was severely close to regurgitating.. there is no such torture!) was to just open up the window for fresh air and lean my head back with eyes closed until we got back on the ground (the last part if the instructor takes the controls.)