Yep – best advice go see a good sports physio.
I picked up peroneal tendonitis earlier in the year when I upped my mileage a bit too quickly. Previously had no problems running up to 40-45 miles a week but moved up to 60 miles a week off after a break in training and the tendonistis kicked in big time.
I messed around for a month resting and dropping mileage but I was struggling to run 2-3 miles without significant discomfort.
I had a 1 hour consultation in which my physio highlighted a number of issues such as weak glutes, adductors and quads. Following that I did a further 4 sessions and was back running again within 4-6 weeks.
In all honesty it was one of the best investments I’ve made, despite having a vastly reduced weekly mileage whilst seeing my physio she managed to iron out a number of biomechanical issues which led to me running faster PB’s within a month of getting back in to full training.
The key thing is being consistent in your rehabilitation and then carrying those practices on after, even after 10 months I still perform my stretches a couple of times a week and have yet to have any reoccurence of the tendonistis.
Best of luck getting it sorted out!