There may be one quick fix your mother may have been telling you your entire life: "don't slouch!" Try to keep your back straight and you won't have to strain your neck as much to look up. It's helped me; my neck used to ache pretty bad (now just kinda bad). It can be difficult to keep your back straight when tired, but I believe it's probably the optimum position to be riding in anyway. One "problem" I've had is that the habit has carried over to my life off the bike; I'm standing and sitting up straight all the time now, and it's kinda weird