My first bout with sciatica was 6 years ago. It took about 6 weeks to feel fairly normal again. I walked the Frances from SJPP and on to Muxia/Finisterre in 2016 with no problems.
However, about 2/3 of the way through my second Camino this spring had me suddenly immersed in great pain.
I was on the Meseta when it began and struggled for a few days before I got to Leon. This forum helped me get some treatment there, I was given a big pain shot and some pain meds (OTC stuff) and told I could resume walking after 2-3 rest days.
I ended up going home early, I just could not manage walking.
While struggling along, I had googled exercises on my phone and they helped. Now, several weeks later, I am totally pain free. The best exercises I found were called piriformis stretches. I did several variations morning and night and they helped a lot.
Oh, and one more thing: the doctor in Leon said that it was a repetitive stress injury. Both of my experiences with sciatica taught me that wearing a pack was an issue (the first time I was carrying heavy books regularly every day). On the Camino my pack was relatively light, but this last time I only could do light walking when I sent my pack ahead.
You may want to talk to your regular doctor about preventative measures, get friendly with exercises, watch what you pack, and research sending your pack ahead at least some days.
Buen (pain free) Camino!