Piriformis muscle/sciatic nerve pain

I’m a 37-year-old female, and I was recently diagnosed with a herniated disk and referred to a physical therapist.
My therapist feels that my sciatic nerve pain is a result of spasms in my piriformis muscle and started stretching me to relieve the pressure on my nerve. During my third session, he stretched me until I had tears in my eyes.
The therapist said that he has to stretch me until it hurts and then go a little farther.
I went home, only to notice my ankle swelling within an hour. Both my ankle and hip swelled, and I was lying on the floor in pain for the rest of the day.
I immediated began icing both my hip and ankle.
I called the therapist the next day, and he said that he probably overstretched me and that I should start feeling better in a few days. Four days later, I was still crawling on the floor, unable to put weight on one leg without the use of prescription painkillers.
I went back to my doctor, who said I have a slight ankle sprain.
The sprain is nothing compared to what I’m feeling near my tailbone.
I am only able to sit and stand when taking Anexia and Flexerol regularly.
This should heal in time, but is it common for this to happen after therapy?
I was almost back to normal activity when the therapy started. Now I feel like I’ve taken a huge step backward.
I also had no knee or hip pain prior to this therapy session. Once I’m healed, will moderate stretching at home be of any help to me, as I don’t feel that I will be brave enough to see a therapist for a long, long time?
Is this a normal setback for my type of problem? Thanks in advance for any information.