Hi, Kara ~
I underwent Retrosigmoid AN surgery in 2006 and it took the incision site approximately a month to heal. However, it took close to a year for that area of my skull to feel relatively normal again, although it still retains a sensitivity that, while not a problem, is noticeable to me. As individuals, some folks will heal faster than others.
However, if the incision site does not feel 'right' to you after more than 2 months post-op, you might consider consulting another doctor for a second opinion, just in case there is some underlying problem not yet visible. Your skepticism regarding your doctors opinion is justified. Physicians are not infallible and have been known to 'miss' things that later caused their patients grief and could have been corrected if caught in time.
Post-op dry mouth and imbalance are not terribly unusual and should eventually subside. AN surgery is invasive and the various nerves involved take time to rebound. When discussing AN surgery healing, remember that time is on our side.
Jim