Welcome Jaz, 3fc is a great tool for helping to get on track. Sometimes I just browse around different forums and read, lots of great stuff and great people on here.
I'm wondering if you might try focusing on either changing your eating habits or starting an exercise program, get that going and then add in the other. I've found that approach has worked for me in the past. I started with exercise and then worked (always working) on eating healthier.
If you need to be all or nothing, challenge yourself to stay on your program for longer than you did last time and if you fall off challenge yourself again to just try and stick with it longer than you did.
I'm doing c25k, too, just finished week 2, trying to just focus on completing the next days workout and hoping to make it through the whole 8 weeks, determined to do it, so if I fall off, I'm going to try it again, i feel so much better just at week 2...
Best to you and as they say, don't quit