Well, 3D tickets are more expensive, so theaters favor the 3D showings over 2D. At my favorite movie theater, the recent Tintin movie was showing in 3D in two of the best projection rooms, at all hours, while the 2D version was only showing at midday, on a smaller screen, with less performant audio. I went to the 3D showing, and had it definitely confirmed I'm one of the people that get sick at 3D - had to leave about midway through the movie, and I probably won't try another 3D show soon.
It's too bad you get sick watching 3D, but you're still whining. I usually throw up when I go out on boats, but I don't whine about it. I just avoid boats. There are plenty of other things to do.
You could try writing a letter to the theatre asking to screen 2D movies at better times. It's worth a try. It's also worth talking to your GP, because it might be something you can solve (hopefully without any medication).
3D tickets are expensive because it costs a lot of money to make a 3D compatible screen and the projectors aren't cheap either (you basically need two projectors, perfectly synchronised, and the screen needs to preserve the polarisation of light bouncing off it, which is a very rare property).
And the sad part is, I really don't think it 3D adds much to most movies. It does give Lucas a chance to reissue "Phantom menace" in 3D, but I wouldn't count that in its favor :)
Now on that point I disagree. Sure, you don't need 3D to convey a story, but by the same token you don't need colour either. Comparing 2D to 3D is like comparing black and white to colour.
If phantom menace was re-created in 3D (and if they did a good job of it) I would absolutely watch the 3D version. I've watched the flying scenes in avatar in 2D and 3D, and in 2D I almost wished for a fast forward button, while in 3D it took my breath away. Literally. I actually *felt* like I was a thousands of feet up in the air.