Temporary far-infrared sauna help, please

My husband set up 2 FIR (Far-Infrared-Sauna) heaters (750 watts each) on a piece of plywood, which we then put at the end of a narrow hallway and hung drop sheets around to make a temporary sauna for me.
He wants to build a sauna of masonry, with 7 or 8 emitters, under our terrace in the new house we are building, which we should be moving into hopefully by the end of September.
I have used the temporary setup 3 times now,(remembering to shower afterwards) and although the thermometer reads on average 100 to 110 F, I'm not sweating anywhere near as much as people say they do. I remember to take a sachet of Potassium/Magnesium/Calcium/Sodium before each session and drink plenty of spring water; however, I realized that on the 3rd day, I was so exhausted by evening I could barely drag myself to bed, and seem to have a Fibro flare-up.
According to the information in Dr. Roger's "Detoxify or Die", some people take awhile till they're able to fully sweat, due to damage from chemicals and/or heavy metals (I think I have that right), and I'm wondering if I'm possibly recirculating the toxins back into my system, by not sweating enough yet.
Any ideas on this would be much appreciated, as well as thoughts on building a permanent sauna in our new house. We decided on brick because we live in southern Spain, where wood tends to be quite a bit more expensive.
Thanks in advance,
Elizabeth Tweet