Hand advice -- switching from steel to nylgut

Hey all -- I've been playing two-finger thumb-lead for a year and a half, on a Goodtime with steel strings.  I wanted to try out a completely different sound profile, so I ordered a Prust tackhead, fretless, with nylgut strings.  It just arrived this weekend.  What a beauty.  I can't stop playing it!

I've noticed, however, that my picking hand has started to hurt.  A vaguely arthritic pain near the top, between the knuckles and the wrist.

I was wondering if any of you have experienced something like this before -- switching from steel strings to nylgut strings and experiencing some hand pain?

And if so, if you have any advice about how to approach nylgut strings differently?

My guess is that I might be picking too hard...

Thanks for any help!