I've not noticed any difference between aft or forward seating on a plane. What gets most PAX is the turbulence, and that's going to be plane-wide of course. Perhaps sitting directly over the wings does help as others have suggested, but I'd suspect not by much.
Most OTC motion sickness only serves to make you drowsy, as well as nauseous.

Have you tried Ginger? This is what the Romans used to feed their Navy (or Roman soldiers that were subjected to crossing large bodies of water - Navy is probably very kind term) to combat sea sickness. It works. At least it works for me. I eat some ginger (supplements work too) and I'm fine. Have not had a bout of air sickness in a long time. I used to take it when I went glider flying with a friend whom was into crazy aerobatic non-powered flying. After about 10 hammerheads and 30 wing-overs, I would lose my lunch, unless I ate Ginger.

I am prone to sea sickness in big waves, and Ginger really does help me.

Just a though.