I want to quit smoking. thinking about doing chantex. this will be my 3rd time trying it. will it still work the same?

Probably: There is no reason to believe it will work any differently the third time you try it. I presume it helped you quit the previous two times or you wouldn't be thinking of trying it again. I don't believe there is any data suggesting that is a bad idea to try again, especially if it is has been some time, a few months, since you last used it. If you think it is your best shot, go for it!

Yes, however...: This reminds me of the old joke "Quiting smoking is easy. I've done it dozens of times." If Chantix helped you to quit before it should work just as well this time. What seems lacking is your determination to not start smoking again. I hope you can find the willpower to remain a non-smoker this time. See http://whyquit.com/ & http://www.shareguide.com/smoking.html for more support. Good luck!