My hair's confused. i need help?

my hair used to always be pin straight. there wouldn't even be a single strand that was wavy. i thought it was because im asian and most asians have straight hair. then in the 7th grade the front part of my hair began to curl just by itself. now my hair has waves and some spirals curls in the front but it is still straight in the back. is there a reason why this happen? i never used to straighten my hair until this happened. i also noticed my hair half way down my back and then i cut it to just above my shoulders in the middle of 9th grade, the front became even more curly. now there are days when the front of my hair is severly curly and/or wavy.