In reply to elliot.baker:
I get this sometimes, nothing to be worried about I don't think, you would probably know if you had a pulley injury. Sounds like you have just slightly over used it, I'd make sure you rested it for a week or two and after that don't climb anything fingery, just pick out climbs with jugs or slopers for a few climbing sessions.
Saying that if it persists then there is a possibility you may have a minor pulley injury and this article will be off help.
http://www.ukclimbing.com/articles/page.php?id=6193