Why is my dog acting strange?

My dog has been acting really weird the past 3 months. One day I got out of the shower and went into the dining room and she was barking at nothing, she then sort of pushed me upstaires, so I did. She kept barking at things for nothing a few times too. Today, I went downstaires to go to the toilet and she was looking at me when I was coming down the staires, She then went into the kitchen and was standing at the back door because she wanted to be outside (to do her business I presumed). When I got back from the toiled she'd done nothing and was just standing in the garden and she wouldnt come back inside, so I had to pick her up and take her back inside. As I was taking her in she was crying. Then I went back to my bedroom and she watched me upstaires. About a year ago she had a cancerous lump on her back, is it still there and gone to her brain? or is it somthing else? I'm really scared