My hair has done exactly the same thing! Was reasonably curly as a baby, but as a child and into mid teens it was poker straight. Over the last 1 1/2 years however, my hair has developed a very definate curl - so much so my friends asked if I had had a perm! I asked my hairdresser recently why this had happened. She said it could be hormonal, a result of some sudden stress or trauma, a result after pregnancy or it could just be one of those things! However, I am absolutely loving my new hair and embracing my curls! =)