I have numbness on the left side of my genital area. what is the cause, and how do i treat it?

Depends: Could be neuropathy from diabetes, problem at 3rd sacral spinal root, a pelvic mass (benign or malignant), or other things. You "treat" this problem by identifying the cause and if possible removing it. Some causes can be "treated, " others (e.g. Diabetic pudendal neuropathy) can't. At your age, you need to be examined. What does your doctor say?