After fever start physiotherapy treatment. It can be due to medication so consult ur docter. And due to weakness

What is the temperature, do you have pain near operated area. If your post op dressings are fine, then probably fever is not related to the surgery. It is likely that you were operated under spinal anesthesia, in which a needle in back is used to make legs numb. You may have post spinal headache. For that rest, plenty of fluids and occasional pain killer too will help, but it takes time Consult with me or other Orthopedic for wound inspection

For your fever, you can see your surgeon again. for uneasiness and inability to sleep , you can visit some physiotherapist who can initiate mild foot exercises. take care and have patience