She is always pushing me away from her. She used to not do that. Why is this? What has happened?

Sounds like you may be coming on too strong and she's not as into you as you are to her.
Back off a bit , if she likes you , she may just let you know. If not leave her be and keep your dignity.

How old are you? Or at least your age range?

There may be many external factors contributing to this, asking her if anything is wrong would be a good way to start