My hair isn't straight anymore!!!?

When i was small my hair was super straight! Then got a hair cut before going to 6th grade and my hair ended up horrible and all frizzy! Now i am in 7th grade and i got a short hair cut and my hairs from the bottom goes up! I was thinking if there is any way to get my hair back to ists straight healthy self before my hair grows long again! My hair is almost near my shoulders and its brown and i use a hair straightner. Please help....