I Have A Stiff Neck And Can Not Use Full

I have a stiff neck and can not use full range of motion to turn my head left or right. I have had migraines for 11 years. I feel like my vision is sometimes somewhat blurry, but I have 20/20 vision. I also get dizzy know and then. I did have thyroid cancer in 2010 and had a full thyroidectomy and radiation. I have been seeing a chiropractor for ongoing treatment for a month now and I'm not feeling better. I am also a certified in personal training, nutrition and exercise therapy. I practice yoga and lead a healthy life. not sure what else to do.