The Secret Diary Of A Call Girl star said she was so worried about her career she is thinking of moving to the US.
The star, 28, who has filmed her last ever ITV2 series as hooker Belle de Jour, said: "I'm just trying to find a job. We're back to the drawing board.
"It's frustrating, it's tiring. It's desperate. You slightly lose your mind. You have no confidence, then you have too much confidence. It's an endless frustration.
She added that TV shows were changing after the credit crunch put the brakes on lavish spending.
Billie said: "Things are getting made a lot faster for less money and there are a lot fewer opportunities for actors.
"There's not a lot of work in the UK - that's why everyone's moving to America.
"It's where the work seems to be. But it definitely feels like a lot more of a slog to get a gig these days.
"I suppose that's a lot to do with our current climate and financial messes. People seem to have to work harder with a lot less time.
"And the subjects people are talking about, the stories they are wanting to tell - they have really changed too.
"There is a pool of work that is really, really thought-provoking and real.
"Then the extreme side is the enormous budgeted studio productions which are basically all made using a background green screen."
Billie, from Swindon, Wilts, moved into acting after a successful pop career and played Doctor Who's companion Rose when the show was relaunched in 2005.
Her hit series Secret Diary is now being screened in the US on Showtime.
She told Hollywood Reporter magazine that she admired the way Americans made TV shows.
Billie added: "I like the way that if you're on a long-running show and you know it inside-out, you often have an option to produce or direct."
She admitted she was keen to land a role on a major US series like fellow Brits Hugh Laurie and Eddie Izzard.
Billie, who has a son Winston with posh Lewis star Laurence Fox, added: "If the right thing comes along and I get the opportunity to be cast in it, then I'd love to do that."
