Are you mixing up your rides - longer / shorter / faster / slower / hills / flats? Does your training include recovery rides and days off? Changes in diet / sleep? Sickness? Weather conditions? Keeping track of all the variables will help you peak for your goal on the 30th.

Some days I feel like I can ride forever - next time out I get worked. Maybe I get overconfident and push too hard out of the gate. Humbling when someone blows by me on their fully-loaded commuter and I'm sucking wind 15min into my ride. When I doubt I blame the wind.