Bummer Ben, hope it sorts itself out.
If you where closer I'd recommend the halls head physio. He windsurfs and understands most of our problems, he's sorted this old body out a few times.

Quite often with this sort of thing, stretching in the opposite direction helps.
How painful is it to stretch you toes out straight???
If it's only a bit more uncomfortable, try doing that 10 times for about 10 sec twice a day. It's only a guess, but may help as long as it doesn't hurt

Ben, i had the same issue yesterday as well for the first hour or so.
i ended up moving the mast base aft about 40 mm and the problem was solved. i guess its a balance thing involving mast base possition and boom hieght.couple this with using weedys i have found i need to change these items a bit to compensate with the centre of lateral resistance moving further aft which is what happens when you use a weedy.i guess in theory the rig needs to move back as well to rebalance,this is prob also apparent when sailors claim they struggle to sail up wind when using a weedy.
i know you where on your new board so it may be worth while experimenting with the mast foot position and in turn boom hieght.
hope this helps maybe some one else has a different theory, i can say coming from using 'normal fins' for decades to using weedys for the first time this year,i have had to make some adjustments in rig position to cope.
of course it could be just a case of needing to 'TTFU'
p.s well done on the distance pb

Thanks for the tips Snides and Elmo, think i need to take more notice of my rig set up.
Crazy thing is that all day i was continually tweaking my kit and it felt really good and i did not have any abnormal soreness and i felt really comfortable, perhaps i just need to TTFU

Maybe try dropping a fin size. Ive had similar sort of pains from trying to keep the board flat when the fin is over powered.