You know the reason behind your pain. It's wrong posture. Don't sit in wrong posture. Use pillow which gives you good support while sleeping on one side and doesn't allow neck to tilt on one side. Start neck exercises to increase mobility and flexibility along with strength of neck. That will help.

Begin daily gentle stretching, including neck rolls and shoulder rolls, once the worst of your pain has subsided. Gently tilt, bend and rotate your neck. Warm your neck and back with a heating pad or in the shower or bath before doing these exercises. Your doctor or a physical therapist can instruct you in doing these exercises... Reduce inflammation by applying cold, such as an ice pack or ice wrapped in a towel, for up to 20 minutes several times a day..consult orthopedician...