I've never felt sick during normal flight, but I have frequently felt sick during aerobatics. Nothing I've tried prevents this (eating bananas, mints, small sensible lunch, no lunch, lots of lunch etc). I haven't tried anti-sickness pills, but since my daughter recently bought some for a 4 day yacht trip I might give one a try next time. I do suffer from overheating very easily, so I always have the vents fully open and wear light clothing.
What I have found invariably stops me feeling sick is to drink a pint of full-fat cold Coca cola as soon as possible afterwards. I tried not doing this one evening and regretted only having a carrier bag with holes in the bottom in the car on the way home.