It can be due to muscle strain coming on shoulder plates due to bad posture and weak muscle. So for pain relief use ice pack or hot water bag for three times a day 10 min-15min or ointment like volini gel or pain relief spray.
After that need to streches back stretch, pectoral stretch, trapezius stretch counting 10rep with hold counting 10.strengthening exercises for shoulder and back. Neck isometric exercises regularly three times.
Next Steps
Avoid lifting heavy weight.
avoid long use of laptop or computer.
always take a support of pillow under neck and back.
take a break inbetween your work. and do stretching.
Health Tips
For more details please consult physiotherapist with practo.