My left thigh has been going numb when i sit, how can i stop it?

Difficult to do: Good chance you have a condition called meralgia paresthectica. It is compression of one of the nerves that comes over the pelvic bone. Usually gives you a numbness on the upper lateral thigh. Can be due to weight loss or gain, and/or constrictive undergarments. See an orthopedic doc or neurologist to confirm the diagnosis. Injections occasional help surgery rarely indicated.