I agree that the bike is too small for you, but I'm not sure a larger size will help correct the neck issue. I try to rest the neck by bending my neck forward and looking down at the road (as safety permits) periodically. That, and riding more help strengthen the neck and the resting, head down position gives much needed rest on longer rides. My neck hurts and gets sore earlier in the season, takes a month or so to strengthen each year.