I’m 15 years old and my teeth aren’t exactly white, i’m thinking of buying some whitening strips product ( not the floss, or any of those other stuff) so which ones would you recommend? Also it has to be available in like a common store like walgreens, or something cuz i can’t shop online. oh ya i forgot to ask is the crest whitening strips that makes your teeth very sensitive a big problem? and does it have a long term effect?