Posterior ankle pain w/ plantar flexion; constant feeling of instability; joint feels like it needs to pop; history of ankle sprains. suggestions?

Ankle impingement: Hi, This could represent posterior ankle impingement. I would book in to see a Foot & Ankle surgeon. Clinical examination is often enough to confirm the diagnosis although to determine the exact underlying cause an MRI scan is generally required.

Ankle sprain: It sounds like ankle instability - see your podiatrist for assistance ! best of luck