mental/physical concerns, zero self confidence, sex drive...

I am a 24 year old college student about to graduate.
I have zero self confidence, sex drive is gone, athletic performance is low, I feel depressed pretty much all the time. Could there be something medically wrong with me? I am confused on wheather this is stress related due to a missing purpose in life, or pressure from school. Or if maybe I have low testoerone levels or what. Any advice would be much apprecited as I am having a rough time with all this. I have no good reson to feel this way, and that is why I am concerned. I have a great family and girlfriend of 4 years. I am about to graduate from college in two months, yet I feel worthless and down most of the time.