Welcome at HCM.
I have red complete details of your question.
It looks that you had injury
to your thigh.Your details show that most probably you had strain of your thigh muscles which has almost recovered.
The present swelling at posterior aspect of knee does not looks to be due to this injury.This can be a baker's cyst
,this is a swelling which may contain fluid.
At present you should do following to have relief-
-Take a mild analgesic
so that you can have relief in your pain.
-Do warm fomentation at your thigh.
-Avoid walking too much & putting excessive strain at your leg.
-For knee you should consult to a orthopedic doctor ,he may drain the cyst at your back of kne & inject a steroid
in this.This will give you relief in this.
Hope this all will help you.
With best wishes.