First, I hope you are under the care of a neurologist, preferably one who is experienced with CES and lower back pain.
Second, and this suggestion is usually disregarded because it is so simplistic. Buy a couple of thera-bead pads that you zap in the microwave for a minute or two. They emit steam and for some reason the intense steam heat provides rapid relief from the unbearable pain in the lower back and legs. Apply it to your lower back, if necessary put a bath towel between it and your back as they can get too hot if zapped too long. These pads don't need electricity or batteries, they are activated by microwave heat and are dry between uses. Some of us keep one close to our recliners because the relief is so rapid compared to pain relieving medicine and are not addictive. They are not expensive, can be ordered over the internet if not available in your locality. Well worth trying and not much to lose except pain! I've had one for over 20 years and it is still in use. They do cool down so a second one allows for longer treatment. The leg pain comes from the agitated nerves in the back so the steam heat helps with that also.
Good luck, you are not alone. Plenty of us still around telling you there is still a worthwhile life to be led once you learn how to cope with the pain.
I had the wonderful experience of the electric type shocks as well. They didn't start till about two months after my surgery. Went the first year with it happening so often I was getting almost zero sleep. Started meds second year and it has cut down the frequency. Tried many things.... Distraction, try not to focus on the shock location, loud music, exercising, reading, changing your location. Try to get you mind away if that doesn't sound to bizarre.
I'm starting to think it may be trapped gas and constipation may play a role in aggravating the damaged nerves somehow.
I wish you well and always remember while shocking, it will end.