I have some thick, curly/wavy hair and it's so annoying what do I Do?

I tried using a straightener and it works i guess but only for a few days. i used to have straight hair to my waist but i cut it to my shoulders a few years ago and-boing-sprung back up. i really wish my hair was straight again. i used something in a bottle or something at walmart a while back and for one day my hair was nice and straight and not so heavy(my hair gives me a headache sometimes; but it's only about midway down my back) so is there something i can do to straighten it and keep it straight because i hate having such thick, curly/wavy hair. i wish it were thinner and straighter. everybody simply LOVES my hair, but i sure don't. what should i do?