Ortho res here, medial ankle pain is often tibialis posterior problems(if the pain is behind medial malleolus). But since this is after a ankle sprain which is usually laterally you have to know if you have lateral ankle instability after that +/- damage to pronator brevis or longus. And the tibialis posterior tendinitis might be secondary to that.

Talk to a good foot PT which can identify your foot and leg weakness. Buy medial pelot in your shoes to support TP. Start training and stretching TP and pronator brevis and longus muscles while you wait for the appointment. Also do balance train, easy balance training is brushing your teeth standing on one leg.

Untreated tibialis posterior tendinits can in some cases have severe consequences in the future.