Hi... In your question I feel like muscle pain is not due to overuse.. its likely to be a pain that might be due to some neck issues as well.. get it properly assessed by an Ortho or by a qualified Physio to know the cause of pain..
Next Steps
As u have pain u can apply ice wrapped on a cloth or via ice bag over the shoulder and neck.. frequently
Health Tips
keep ur neck properly supported during sleep and avoid using too high pillows..try using a rolled towel under ur neck... if you are sleeping in face up position.. else fill the gap between ur shoulder and neck with pilllows.. avoiding prolong bending of neck to that side...