The degree of the swelling is an indicator of the severity of the injury. The injury you describe could be a more severe sprain or possible fracture. See a doctor.
Swelling, bruising, and inablity to bear weight on the ankle is a sign of both a sprain and a fracture. The only way to know if you have a sprain or fracture in your ankle is to seek medical attention so a doctor can examine and treat the affected ankle.
An ankle sprain or a fracture can both be very painful. You need a professional medical opinion and the sooner the better. Don't risk your good health.
The only way to tell for sure is to see a doctor and have an x-ray. Pain levels and swelling can vary and are not a reliable way to determine the severity of the injury.
