I suspect that the detoxed halide bromide as well as heavy metals like mercury are being dumped into the kidneys and they are having a hard time with the detoxing. Salt pushes (see http://www.breastcancerchoices.org/iodineindex.html
for protocol and how to do salt pushes) will help flush out the bromide and heavy metals. Kidney and liver herbs or the amino acid NAC will help the liver and kidney with the detox process. When I am having a tough time with detox symptoms, I take 2-3 caps of NAC 2-3 times a day. If you're having a hard time with the salt pushes (use unrefined salt) put the salt (1/4-1/2 tsp) in a BIG glass (16oz or bigger) of water so the water only tastes mildly salty or put it in something like sodium free tomato juice or put the salt in a capsule and follow with at least 8oz of water. I make up the capsules for my daughter because she has a hard time drinking the salt water.
Once you start the salt pushes and take the NAC, the low back pain and bladder spasms/pain will resolve.