I know people who have had significant hair changes after chemo for cancer. Blonde becomes dark, straight becomes curly, etc. So I would think hormone changes could do this too. Or nutrition.

I have naturally curly hair. When it is longer, it is straighter unless it's humid out--then it's unbearable FRIZZY! When it is short, it curls more. So, go ahead and crop it, girl, I think you'll have even better curls!