White marks and braces!!?? :(?

I just got my braces 2weeks back...and I have been noticing these small white marks(or something like that) which are beginning to form on some parts of my teeth..any idea what they are? And i do brush my teeth around 2-3 times a day followed by Listerine ! So what can they supposedly be? And for those who have had braces.. When did u start noticing small shifts in the position of your teeth?? Will it take months for teeth to start shifting ? My teeth aren't that bad if that helps... just an overbite which isn't that bad either..Just anxious.. Thanks ! :)