hi piet your description of 'pop on the side of my tibia(medial side) about 4 inches down from my knee.At the same time I felt a funny feeling in the back of my bum'
by running in the straight leg position could suggest that you have also strained the neural tissue or fascia running up higher than just your calf. this would need to be asssesed and rehabed also, otherwise the calf will not respond well. also the ankle sprain will nedd to be fully assessed and rehabed.

good luck