In reply to Dave Garnett:
Ergo 'meta-arsalgia': beyond a pain in the arse...
To the OP... Something similar has bugged me seriously for 3-4 years, though I've never had a diagnosis. Never much swelling, just pain! Main joint, big toe. It hit home when, on a trad route within my grade, the pain got so intense I decided to jump off and take the fall rather than wind it out (no matter, it was only Wilton, but it did knock my confidence). Slabs went from being my speciality to things to be rationed, which was demoralising (I'm crap too, and always climb/ed better on the slabby stuff). Cracks became more nightmarish even than slabs.
Sensible advice? Good-fitting lace-up shoes help, as does ibuprofen gel. Lay off for a bit...but you're not going to do that on a long trip are you... Maybe take your 5-tennies for seconding on long routes.