That's another common skater muscle pain area, in our case usually caused by skating too much too quickly. This muscle plays a key part in skate control, edging, and pro/supination.
I reckon it's something in your bike fitting, as posted above. If it were my pain, I would try the following:
Paying to see a sports physio privately. Not cheap, but you only get one body and it's worth looking after.
Getting a bike fitting session with the bike whisperer, Scherrit.
Doing lots of edge control exercises, such as standing in your bare feet and rolling your knees and ankles in towards each other, and then out again. The floor contact point in your feet should roll from one side to the other whilst doing this.
I am not an expert though, so don't take my advice, nor any internet advice since it might well be totally useless or even harmful for you.