Why has my hair lost its natural wave?

my hair used to be a little wavy where i could scrunch it and let it air dry and it would be fine or let it dry over night and it would be wavy. but for the past 6 or so months now it is loosing its wave? no matter whatany more. if its wet and i scrunch it wont stay or if i have it in a bun when its wet i'll take it out and still will dry somewhat straight. i got a new straightener for christmas and i do use it often and it works good and makes my hair pin straight its a wet to dry straightnener as well but i dont use it when my hair is wet. could my wave be getting lost from using it too much? my hair is really really long to, like to almost the end of my back. what can i do to get my wave back? please help i really miss it! thankssss