I have a hard time sweating too. On the most humid day in summer, if I'm lucky, I might get a little dampness on my upper lip. This, however, is not healthy apparently.
I have recently started taking "sweat baths" and the secret to my success is that I put a heater in the bathroom and get the air quite warm. I run a hot bath (with 1 cup Epsom Salts , one cup baking soda - and about 3T powdered ginger) - as hot as I can stand to get in - and then run more hot water once I am immersed. I also drink cold water while I am in the bath. After about 5 minutes, I find I am really sweating.