It is hard to diagnose, as we need more information. Does it hurt at the front, sides or back of the shoulder...
Generally shoulder problem hurts when you lie on the bad shoulder. Other areas like the neck and upper back could refer pain too...
Generally pain at the front of the shoulder may respond well to icing with towel wrapping on area of pain for 15 mins. You could do this 3 times a day.
If the pain has come on slowly with no obvious cause, it could be frozen shoulder which could take around a maximum of 6 months to get out of the pain stage. It could still be stiff after but with minimal pain.
You will need a physiotherapist consultation for a clear diagnosis and treatment.
Next Steps
You will have to get medication from an online consultation with a General Practioner.
Health Tips
Avoid lifting, pulling, pushing at this stage. **But use your arm to avoid stiffening (in pain free ranges)....