There's been quite a bit of discussion on the cyberpluckers list about this, also articles in Autoharp Quarterly. I suspect the FAQ on the website [autoharp.org] would also have info. Bryan Bowers stresses good ergonomic positioning.

I've even taken my harp/strap to the chiropractor's office and ask her what I needed to change. She recommended piano. [couldn't resist that, sorry] You shouldn't stoop over, which for most folks means wear it high [shorten the strap]

And I think Bill D is on target when he mentions your chord bars and felts- sounds like you need to have the action lowered so that you're not having to strain so. There are several folks around who can do this for you if you like. Hope you get some relief soon!

T