Hello,
Arm pain can be due to various reasons.The most common is muscle pull due to any injury or even bad sleeping postures.
Hot packs alternating with cold packs taken for total 20 min can help to some extend.
Rest is required.
Next Steps
Since pain is not subsiding since 2 days it would be good to get BP checked
Health Tips
good if you visit an orthopedic or a physiotherapist for better assessment