Inflammation with the bursa guiding the heel known as Retrocalcaneal Bursitis. Repetitive stress or friction over the back again in the heel leads to the bursa to swell causing heel pain and tenderness, swelling and ankle stiffness. Generally linked to Achilles Tendonitis and Haglunds Deformity.   "three days in the past https://www.theorthopaedicandpainpractice.com/the-definitive-guide-to-diagnosing-and-treating-ankle-pain-in-singapore/