My girlfriend is driving me mad

She is evasive and is vague about her finances and her past.My brother has already labelled her "tricky" and I think he's right.

What also annoys me is that she likes to play mind games. She tries to trap me and trip me up. At the moment she's jealous of a perfectly innocent working relationship I have with a female colleague.

She thinks we're having a sexual affair, which we are not.
Twice now I've caught her sitting in her car outside my work trying to spy on me.