My 9 year old daughter has become very moody over the last 2 days?

Hopefully you can get some good answers on this one, I have been trying to figure the same thing out with my 9 year old girl. She is soooo dramatic and everyday Come's home with a " Today was the worse day of my life!" then attitude, attitude, attitude. Whiney, moody, then happy and lovely..then start again. I even took her to the doctor because I thought maybe she was getting ready to start her period. He didn't think she would be starting really soon because she isn't developing much anywhere else yet...but he said things can change fast. I think its just age, and the blessing of having a girl lol. Good luck to you!