Have you been carrying bag on that side .. or sleeping in an uneven pillow .. have you had a fall in that side ..
If your pain is from neck to shld.. Most likely to be trapezius spasm.. which can be treated with Physiotherapy
Next Steps
Kindly pls visit a physiotherapist for the same
Health Tips
Follow good neck posture while doing work and do chin tucks as much as possible which would be taught to you in a physiotherapy session