What Causes Numbness On Feet?

I'm 26/f and I'm overweight. I'm trying to lose weight and get back in shape but whenever I do a workout on my elliptical my feet go numb and I have a hard time finishing the workout. Then sometimes when I sit on the toilet my foot goes numb, usually my right one. What could be causing the numbness in my feet, primarily in my toes? Also, I play softball a couple nights a week and recently I get really bad pain in my calves on the insides of my legs. The pain can get so bad that I can barely walk. What could be causing this?