It can be neck and back muscle spasm due to poor posture (sleeping, sitting, reading, lifting). If u have a desk job that requires you to sit and use computer/write for a long period then it may attribute to you condition. Try pacing your activities so that you can give yourself a break from the acquired wrong posture.
Next Steps
Visit a physiotherapist for proper management and postural correction. Neck and back stretches followed by warm water fomentation will help.
Health Tips
Avoid excessive bending and slouch posture.