In a way, it doesn't really make any difference, in that it's not (at the moment at least) bad enough to stop me from swimming, so it probably wouldn't change the course of action (rest where possible, try to work on my hand entry problem anyway, and press on with the training). But it's frustrating not knowing what's causing it....and there's always the worry that it will get worse and start affecting my ability to swim.
So, my plan of action for now is to speak to my GP next week (when he's got the letter from the physio), and maybe think about getting the MRI done privately if it's not too expensive if the NHS one is going to take ages.
I've been pretty fortunate overall in terms of injury, so I can't really complain. But I don't like uncertainty, and much preferred my previous strategy of being in total denial about the fact that it was hurting!