Hi, I noticed the color of my scrotum and the lower part of the underside of my penis shaft has dramatically changed color from dark to light. The "feel" of my scrotum has also changed, it used to feel soft like the rest of my skin, but now the skin feels rougher / clammy (not wet) and the hair is barely regrowing. I got checked for STDs and everything came back negative. What else could be causing this?

Thanks in advance.