KeyFragments get more rare each time you get one?

Hell i have been geting hextech boxes every time a new one comes out and i been geting alot of hextech keys around 1 every 5 wins or so but after a while since it started i havent got a hextech key in over 40 wins this is realy fustrating considering i have 2 boxes right now and 2 key frag so i would like to know is this happening to any one else or is it just me casue right now it seem i am going to have to buy key frags to unlock these chest