Minor sprains and strains, back pain, neck pain and or headache should normally resolve within 2-3 days. When pain is not improving in 2-3 days then it is abnormal and you can get used to it rather than fix it. Getting used to a pain stimulus is technically called accommodation. The same phenomenon as when you stay in a bad smell. The smell (stimulus) seems to have gone away but you have simply gotten used to it. Look to consult a chiropractor on day 4.
Pain is a sensory emotional experience that can come on even when no tissue damage has occurred.