My hair always frizzes up!?

my mom thinned my hair like a month ago, and trimmed it and ever since then it ALWAYS frizzes up and gets poofy after i straighten it. its so unbelievably annoying like when i go to school or go someplace it always does it. and its soo rough and i just want it silky or soft even when i use shampoo & condition thats supposed to make it that way. help ?