Hey Pux: I'm no doctor, but I'm wondering if you are not getting enough oxygenated blood to your penis? Are you taking Viagra or another ED drug to increase the blood circulation down there?
BTW -- you should be stimulating your penis manually (or whatever way you can get it stimulated) on a regular basis as well.
I'm sure it's nothing serious, but I would call my doc if I were you.
Regards,
Tom