Sciatic pain immediately after eating

I have had a sciatic pain in my lower back and legs, mostly in the left leg, for 8 years now. Two months ago, I began to eat a largely raw vegan diet and last month, I did a 7 day Water Fast where I lost 8 kg or so. My pain is much better now, better than it has been in years. I can sleep on my back without any significant pain, something I couldn't for some years. I also take a weekly salt water enema.

However, I notice something new for the last 2 weeks. Whenever I have a meal, the pain in my lower back and legs, more the left one, comes back. It is a sensation of tingling and of stiffness in the muscles. It takes not even a minute for the pain / discomfort to come.

What could explain this symptom, and why it is there now? It seems that my sciatic nerve gets irritated when introduce food into the system. There are no particular foods that do this, but the heavier I eat, the more this is the case.

Could anybody offer explanations for this, and possible ways to work on this?