My puppy no longer goes to the door when she has to go out?

My puppy is almost 6 months old and I got her when she was 2 months. She has always been good about going to the door when she has to go potty but for the past two days she hasn't gone to the door at all...she will just go on the floor and the only way I know that she has to go potty is because she will start biting things that she knows she's not supposed to bite. Also, she has been misbehaving a lot and its almost like all of the training we've done has gone out the door. Does anyone know what could be causing this regression?