Serve cold chills can't get warm, muscle ache, sore neck. What could this be?

Flu. Seasonal flu is very common viral infection. Usually the condition resolves on its own with home care. Drink water and get a good rest. NSAIDs (e.g. Aleve) are also recommended every 6 hours. If concerned, see your PCP after 4 days or so. Take this opportunity and quit smoking.