What Causes Numbness On Thigh?

Hi there, Im a 43year old male. Ive been experiencing numbness in my left thigh, usually worse after a day sitting at work. The skin around the middle of my waste is sensitive (like sunburn), i get a burning feeling like a line of fire if I sit in a particular way, which goes when I stand up, and the left side of my stomach and thigh are much colder than my right. Any one got any ideas. Thanks.