Broken Heel and Fractured Talus

On 8/29 I broke my heel and fractured by Talus.
I had surgery on my heel. They inserted a pin through my heel to hold it together.
I am finally walking now, but the pain continues.
I can handle some pain and disconfort. My left to right motion of the foot is not too good.
Also, when I am on my feet “to long” the foot and heel are real sore.
That I can put up with.
But when I sit down afterwords, the pain is unbearable.
I usually have to use a walker to get moving again.
And even then it is not easy.
Why does this pain occur after I sit down?
I have even started my stretching excercises after I set down to stop it from tightening up.