I'm new too but I can relate - I have a birthday that I have always considered momentous coming up in two weeks, and I'm a yo-yo dieter too. Obviously I'm not going to be able to wear a bikini by then, but I cannot imagine spending my birthday feeling so down about myself as I am now. I know that if I start now, at least I can feel good about the fact that I put in effort. I've spent WAY too many years before this feeling so bad about myself, and now I'm done with it. I'm not wasting any more time, and I can see that neither are you!
Good luck - I know that you can do it!