Not necessarily your weight, but probably just the sudden forces involved with a bumpy road. This is an annoyance with carbon parts. Seatposts sometimes slip, bars move, and stems can sometimes twist. The recommended torque is surprisingly small with some of these parts, so carbon assembly paste is the way to go. One small container will literally last a lifetime. It will provide additional friction for the carbon parts. I was a convert once I tried it.

There is a thread in the Road section where one person after another cracked their new carbon frames trying to torque their seatposts properly, but that seemed to be an issue with the seatposts they chose not fitting tightly to start with. In each case, they felt the recommended torque was not exceeded.

@ dirtyphotons: cheers. My harsh stance and poor choice of comments last night should not have gotten personal. My apologies. I had hoped you hadn't read the post I modified before doing so, but apparently you did. Kudos for pausing to think before replying to my ill-considered comments, giving me the few moments I needed to rethink.

To the OP - At least take the time sometime to read the specified torque for some components, and then find a torque wrench to feel what some of those numbers mean. At least then you will have some sort of sense for the feel of the correct torque, and you can likely avoid mishaps due to gross errors when assembling your bike. For all my pontificating, it is these gross errors that will cause problems, not the case where you've applied 48ft-lbs to a crank bolt instead of 55, or 7N-M to a stem instead of 6.