Stop looking for the pen and start looking at the writer. It's not the pen giving you cramps. It's you; your writing style, your grip, everything. You're not used to writing as much as you do, so up until now you've dealt with it. You are likely gripping too tightly and writing too hard (too much pressure).
Personally, I took a handwriting lesson (very affordable) and it taught me so much! How I hold the paper, my arm, my hand. All these were contributive of cramping. I also picked up a few other tricks to alleviate the cramping whilst writing. I suggest looking into that. As pens can be very subjective you'll be buying a box full of pens and still have all the same problems.
If you'd like information on a lesson, shoot me a PM and I can give you the contact information. If not, that's okay too.
Personally, I took a handwriting lesson (very affordable) and it taught me so much! How I hold the paper, my arm, my hand. All these were contributive of cramping. I also picked up a few other tricks to alleviate the cramping whilst writing. I suggest looking into that. As pens can be very subjective you'll be buying a box full of pens and still have all the same problems.
If you'd like information on a lesson, shoot me a PM and I can give you the contact information. If not, that's okay too.