You may be experiencing the start of post-traumatic adhesive capsulitis. This is like having a frozen ankle (similar to a frozen shoulder). Scar tissue forms in and around the ankle. Fibrous bands try to replace any torn ligaments and stabilize the joint.
Unfortunately the body sometimes overdoes it and too much scar tissue and too many adhesions form. Loss of motion from the restrictive tissue sets up a pain cycle early on.
It's best to make an appointment with your surgeon for some follow-up. You may need to resume some of your rehab exercises. The therapist can also mobilize the joint. This may break up some of the adhesions, restore the joint fluid, and ankle motion. If a short course of therapy doesn't change the picture, then surgery may be needed.
The doctor may have to cut the joint capsule and possibly remove some of the fibrous scar tissue. This type of surgery can sometimes be done arthroscopically. This saves you from having large, painful incisions and more scar tissue later.