I need some help with my bunny...?

About a week ago I got a bunny. The store where I bought it from did not tell me how old it is or even the gender. She/he was fine for the first week but now she/he's constantly biting me and I have her/him in my dog's old cage with some cardboard around the edges to keep the wood shavings from coming out. I'm not sure why she/he has gotten all anxiety-like and I need some help. Also, I put her/his food into a tupperware thing but then she/he'll like flip it over and dump it all out. I really need some help!! :(