My dwarf hamster's personality suddenly change. Help?

I got my dwarf hamster about 3 weeks ago. The pet store says she's a Winter White but I've been doing some research and she seems to be a Campbell so I'm not completely sure which one she is. I don't know her age either because I forgot to ask the pet store when I bought her, but I believe she is under a year old. Anyway, when I first got her she wasn't very tame but turned around quickly. Within the first couple of days, she allowed me to feed her and pick her up. Eventually, she would run to her cage door and wait for me to pick her up if she heard me coming in the room. About two days ago, this changed drastically. She would run into her igloo if she heard me coming and never takes food from my hand anymore (even though it used to be her favorite). It's like she's afraid or annoyed of me. This happened within one day. Does anyone know what is wrong with my hamster? Please let me know. I am worried!!