I now have a general unease in my thumb, wrist and arm, and a contraction in my right shoulder, probably the real cause of my problem. I decided I needed to Arnica. Not gel, because that one the many things I get a rash from. There used to be an ointment by A.Vogel with 50% arnica, but now they just have gel, and anything that's transparent gives me a rash within three days. But I asked my pharmacist and she came up with the closest she had to my original ointment: homeopathic, with 30% arnica, and some other herbs. I also have my ice pack ready for when I finish writing this post, and I'm really planning to do stretching exercises before practice tomorrow.
This is going into my clarinet case tomorrow: Traumeel arnica ointment, Theraband for palm stretching (not the official ones, this yellow one is already quite strong), and the softest Handmaster Plus for finger stretching (I usually take the medium strength). And of course there's the wall to stretch my arm. And an ice pack when I come home.