Would a plaster cast be needed for my ankle sprain? it's been 6 weeks it's swollen in pain but my initial x-ray show no breaks

Unlikely: A plaster or fiberglass cast is commonly used for broken ankles. Although you may not have a broken ankle, you may have tearing of the ligaments or tendons in your ankle. If you are still having pain and and an unstable feeling in the ankle 6 weeks after your injury, you should be evaluated by a physician. It is possible you would benefit from exercise therapy or visiting a physical therapist.