"Maybe the detoxifying has slowed down my thyroid?"
I think this happens somewhat due to kicking up Hg and Hg's effects on thyroid, including selenium. Cutler has recommendations for this for those on his protocol.
In my case I've gained 10+ lbs but my clothes still fit. I have a lead and cadmium problem along with bone density problems. A followup Dexa bone density scan reported an 8% improvement in my back which was previously unresponsive to my doctor's supplements and medications. I bet some of my weight gain is due to the healthier density of my bones.