My left leg has gone skinnier than the right, how do i fix this?

ok so i recently was told i fractured my foot and my leg foot was placed in a cast, i find out that it was actually not fractured however there was damage and i was able to take the cast off after a week and a half, its now almost 3 weeks and i can walk perfectly fine, i can run jump etc although my leg still feels a little wierd, however it has lost a lot of muscle around the calve and ankle area and i feel ive lost my running speed. How can i get my calve back to the normal size because this serious annoyd me.