If you fly frequently you should find that any degree of nausea will lessen. But after a period away from flying you'll be back to square one. At least that's what I've read/been told, but I don't suffer myself! It sounds like the heat aggravates it for you, so buy yourself a nice lightweight set of flying clothes. Check out some of the outdoor shops for materials designed to keep you cool. Also be careful about what and when you eat, make sure you get plenty of sleep etc etc.
And good luck!
