I usually get hand cramping when I'm writing with a flex nib and can't complete an entire letter in one sitting. Is there a way to combat this fatigue?
How does the pen fit in your hand?
Maybe it's too thin?
I find that with my thinner pens. I prefer a thicker pen especially with a flexible (or semi-flex) nib.
Pressing too hard Have you tried slowing down? I can write pages with a Noodler's Flex. I just PIF'd it to a coworker as I got an Eversharp Symphony. It just takes a lot of time to fill a page if I'm trying to get maximum flex.