Help! I'm going nuts!!!!

I have a two year old daughter and in the last week anytime we try and change her diaper she's starts crying and fussing saying "no it hurts" she always trying to get outta wearing her diapers. They aren't too tight on her, we've even tried the size up but they are just to big. She's also poking at her vagina saying that it hurts as well. It's a little red but I think it's from her poking at it. I've put diaper creams on it and it helps until she gets at it again. What could be "hurting" her? Does this mean she's ready to potty train? I have the potty out when she isn't in a diaper but she won't go on it.  Help it's driving me nuts every time I change her it's a fight.