How can i get straight thin hair?

My hair is thick, curly, and frizzy :S Its kinda like a curlier version of Kesha lol. Anyway, I keep trying to straighten it but it comes out like a thick afro-ish style. I have to use a ponytail halfway through the day too! I was also wondering if it was because I died my hair from BLond, to brown, to red, and than brown in the last three years. PLEASE HELP ^^ My hair is also dry so if you have any tips for me that'd be great. (What i want my hair to be is straight and thin)