Is there anything that can cause serious ankle pain?

A number of things: Depending on the history of the patient it can range from chronic ankle instability to arthritis to neurological damage. This is something that should be evaluated promptly by a foot and ankle specialist.

Serious ankle pain: Severe ankle pain could be caused by a severe sprain, fracture, high ankle sprain, tumor (giant cell tumor), osteoarthritis, osteochondral defect (damage to joint cartilage), septic joint (infection), gout, osteomyletis (bone infection), foreign body (ex. Bullets), etc.

Depends: There are too many sources of ankle to pain list here. The treatment and the ability to control it would depend on an accurate diagnosis and workup. See a foot and ankle specialist for the right plan.