I have the same problem, which is why I often can't shave everyday, whether it comes to my head or face. I have no real advice since I too have that problem, but you are not alone! When I had my goatee really long, it was always a pain trying to shave my neckline, and get it close and slick. When I had that look, I liked to keep my mustache shaved slick, and my neckline clean, but I usually had to wait a good 3 days for that and even then usually it was still just a bit sensitive to the shave. I don't think I will truly ever find a good solution for my face/neck. Which is why I try to keep a good goatee or beard, less to shave, haha!