I got this problem too and I guess much of it is due to my hanging. My take on this is that our penises get desensitized both physically and mentally because of all the time we spend “touching” our penises. It becomes normal to touch our penises all the time without a hard on, right? Remember the first time I tried to jelq, my boner was so rock hard it was almost impossible. Same with hanging, I needed to jerk off prior to every hanging session because of my penis getting hard just by wrapping it. Well, I really miss the boners I used to have. They were so hard it almost hurt! Damn!
Took an unplanned 10 days off just recently and my sexdrive, erections and sensitivity increased. Not nearly as much as they used to be, but I really felt a difference. I`m also 19 btw.