should i be concerned?

Question
hi, i bought my female hooded rat from a pet shop about two weeks ago, i was told that she was 16 weeks old, i brought her home and had her setup all ready for her. she was very nervous at first. and i feel that ive gained a bit of trust over the past two weeks. she know comes out of her wooden house when i call her and comes and takes treats from my hand. she dont like being handled much, when i do handle her, she seems to try to get down on the floor. she is an active rat and always seems to be getting up to some sort of mischeif in the cage, but recently she has shut herself inside her wooden house and blocked up the doorway with tissue. she doesnt respond to me calling her. i have tried taking the tissue away unblocking the door but she just comes out a tries to bite me. she has caught my finger and im sure its not a full on bite. then blocks the entrance back up. should i be concerned? could she be unwell? or is this normal behaviour?? look forward to hear your response. many thanks. tom

Answer
Was she with males when she was at the pet store?  Have you peeked in the wooden house to make sure she did not have a litter of babies in there?   Nesting and being unusually aggressive is a sign of pregnancy and also new moms do this.  I would take a peek in the wooden house and and take a close look.  Let me know how things look.  If she is pregnant and close to birth, her belly will have a pear shape to it and you will notice her nipples may protrude.  Let me know.