Guys, I have hemachromatosis, and thus, don't produce enough testosterone. Stay with me. Because of that, I take testosterone injections once every 2 weeks. When I'm at the point when my levels are low, before the injection, I find it more difficult to masturbate, and usually give up after a few strokes. After I get my shot, I'm a new man and can't masturbate enough. Woodie every morning.
Moral of the story - get your testosterone levels checked.