What could cause severe ankle pain. No recent injury. It's only in ankle I injured a few years ago.?

See a physician. It may be the sequela of one of those bad sprains or what could have even been a fracture. See a specialist of the ankle for x-rays and examination.
Ankle pain. Since you had a severe injury few years ago and pain is within the ankle joint get checked for osteochondral defect. See ankle specialist and likey get MRI to find out for sure. Had a case similar to yours and it was an osteochondral defect just last week.
Many things. "ankle pain" can be caused by any of the structures that make up the ankle: 1. Joint pain from arthritis 2. Tendon problems 3. Nerve problems 4. Vascular or circiulation problems 5. Ligament injuries 5. Infections see doctor to sort this out.