Yes, if you sleep on your sides without proper pillow support it can be a reason. If this is the case, kindly use a pillow to fill the gap beneath your neck (when lying on sides) and also one pillow can be placed between knees(when lying on sides).
Consult a physiotherapist. Posture correction exercises need to be done. Core strengthening exercises also do half the work.
Next Steps
1. Learn to Relax! We have become habitual of tensing our muscles. This also contributes to weak core. So practice relaxation! feel it!
2. Visit a physiotherapist.
Health Tips
Our bodies are meant for physical activity! Make sure you do them regularly. Any kind of aerobic activity will help. Our postural muscles function better with aerobic activity.