firstly if you do have sciatica
then you need to get it treated thoroughly as 4 years is a very long time, this might lead to permanent degenerative changes in the sciatic nerve
Local bruising behind the knee is unlikely to be due to sciatica.
This might be due to localized rupture of vein which is likely to get resolved on its own.
I dont think you need any active treatment for this. Do cut down on the stretching for a while though.