I have a burning pain in my left arm, just above the elbow. There is numbness down my arm. No other symptoms. It started 3 days ago. What should I do?

Ulnar nerve-injury? Ulnar neuropathy which is associated with elbow pain if injury or arthritis, is the cause, is most liekly. Cervical spine injuries would be much less likely to occur so acutely. See a rheumatology, or physiatry, or neurology specialist. Ulnar nerve compression involves the 4th and 5th digits of the affected limb. (actually one half of the fourth digit!).
Pinched nerve. Numbness and burning pain down arm is pinched nerve most likely. I would get neck MRI and try steroids first. If no better, consider steroid injections.