I'm on day six of my fast and the same thing happened to me, and during the last fast, which caused me to stop: painful lower back pain that feels like a pull and worstens when I stoop over. I got the same pain on day four of this fast. My urine is very clear, so I'm not dehydrated. I also started to see foam or bubbles in my urine since day three. I tried the electrolytes, caster oil pack, Epsom Salt baths, heating pads, bone broth, etc. All provided some temporary relief but the pain continued until it got so bad last night, I had to try something else. For me, it was the SALT!!! I took a half teaspoon of Sea Salt dissolved in hot spring water. A couple hours later, the pain must have subsided since I was finally able to sleep. This morning, the pain is nonexistent unless I do a deep bend (like touching my toes). I notice I don't have a headache today either. I'll continue with the salt protocol today, but use Himalayan salt instead, to see if I can get the rest of the pain to subside. Has this happened to anyone else?