Hi Joe,
I have had similar problems but without the sharp headaches though. I know that poor posture, clenching under stress and stress generally can tense up the muscles especially of the neck and shoulders. Before you see a chiropractor I think you should see a doctor and perhaps get some X-rays to see that it's not something more sinister. I had seen a chiropractor before but I think that they are all too keen to manipulate which can be dangerous and treatments seem to be long, lengthy and end up being too expensive. After consulting your doctor see whether they can recommend a good physiotherapist. I still suffer from chronic muscle stiffness and once was told that the Feldenkrais technique was good- so perhaps find a physio who specialises in this. I found Feldenkrais to be useful more than yoga. Hope this helps. :)
