I feel numbness in penis. Is it due to nerve impingement?

Hello doctor,

I am a 26 year old male. My height is 74 inch and weight is 187 pounds. I do exercise with weights regularly. I have noticed that I have reduced feeling in the skin on my shaft. I cannot feel normal touch, but I can feel the pain if I pinch it with my nails. To best describe it; it feels like my penis is not there when the head was covered by foreskin. I just noticed it two weeks ago. Is this due to nerve impingement? I do not have any back pain or radiating pain down the legs. There is no trouble or pain with defecation or urinating. There is no tingling or pins and needles on the shaft. Rarely, I feel some burning or numbness feeling. I do not notice any discoloration or anatomical abnormalities. Is this a sign of diabetes? But, there are no symptoms such as polydipsia, polyuria, etc. I do not remember any trauma to the penis. I do not ride bicycles at all. I have been to a urologist and done an ultrasound of the penis and testicles along with a Doppler. But, there is no finding to be worried. My libido is very low. I get erections during the night or if I really concentrate on erotic thoughts. I have not tested testosterone levels, but I suspect them to be normal. I do not really mind the reduced feeling in the shaft. But, it would be nice to get it back. I am worried by thinking that it may spread or this is a start of a more serious disease. What is your opinion? Thanks in advance.