Not able to sweat in FIR sauna. Need suggestions

I am taking 1 litre of water before sauna , good niacin and following all the vitamin Dr. sherry rogers suggested in her book Detoxify or Die , but still I am not able to get sweat.
15 min of running producing sweat but not the 45 min's of FIR (Far-Infrared-Sauna) sauna except little sweat here and there. I get enough niacin flush for my 400 mg niacin, get lot of dizzy ness, which disappears once I take post suana vitamins like buffered vitamin C , alpha lipoic acid , glutathoine. I am very traumatised by this lack of sweat. Are there any thing I can do .

Initially I tried 140 F for 1 hr or 1.5 hrs , but I stopped those hot temperatures once I started feeling the dry skin and intense heat related issues.

I appreciate any help,