I always get a stiff neck with a flare. Rather, it is more stiff than usual.
Good advice here already, so again, some heat may help. A hot shower sometimes helps mine. I've become a fan of good old-fashioned Epsom Salt, and there is a brand out there called Dr. Teal's Therapeutic Solutions. They make a Mint and Rosemary type and you might find it in a Kroger if you have one, Walgreen's or possibly CVS.
If the stiffness and soreness doesn't resolve over a few weeks, you may want to let your doctor know. I had this for quite some time and it turned out to be a partoid infection. Most likely, yours is a flare and hope it improves soon! Stiff and sore necks are no fun...