Could be peroneal tendon. I had mine operated on in January and it is still healing. I have pain very similar to what you describe. My PT suggested I wear the night splint I had from PF at night. I thought he was touched in the head but 3 weeks later it is finally improving. He explained the foot naturally flexes down when sleeping and that strains the tendon. So I wear it every night now.
Good luck, the pain at the end of the day is so demoralizing.