The same thing happened to my brother. Me and him both have naturally curly hair. But when he was about 2 he got it all cut off. Then it started to grow back straight. Whenever he grows it out long it begins to curl.
So I think thats what has happened with your hair.
Do you want to have it curly or straight short? I think it would look super cute short and straight!
If that is what you want, I think you should be happy!!! Good luck!!