it is because of the ligamentous injury and creates pain and swelling . ain and swelling subsides with time leaves the muscle weakness which takes time and recovers only by the exercises done by the physiotherapist.
Next Steps
go to a physiotherapist and take the treatment. Ultrasonic therapy helps in healing of ligament and muscle stretched or inflamed,heat(wax) therapy increases blood circulation and TENS helps in relieving pain,Exercises will increase the muscle strength.Do it for at least 2-3 weeks.You will get the relief for sure... take care.