My Dog Has Been Acting Strange For The Past 2

My dog has been acting strange for the past 2 weeks. He goes into to a room and doesn't want me to bother her. When I go into check on her she is shaking and doesn't want me to disturb her. She has had cancer and had it removed about 6 months ago on her back leg and now she has a big hard bump on her behind that grew really fast..within 3 weeks. She is scheduled for surgery in 2 Days. What is wrong with her...she won't eat her treats today??? Concerned and heart broke.