It is not obvious to me that this problem is necessarily an issue with spoke fatigue. Since it is on the non-driveside, I would first suspect uneven spoke tension. I would rebuild the wheel using new spokes. This would get rid of any existing damage to the spokes, and it would ensure the spoke tension is even. I have found from experience (I am a bit heavy for a cyclist as well - almost 200lbs), that when just replacing a broken spoke, it is very difficult to get the spoke tension back into balance.
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter