Thanks for your query.
From description , it seems you might developed muscular or ligamentous strain over shoulder and neck .
Now after 3 weeks if pain is severe ,I would suggest getting this evaluated by an orthopedician for an accurate diagnosis and appropriate management. You may get the MRI
of the area affected under his/her guidance.
Meanwhile following measures will help with the pain
• Anti -inflammatory drugs like Tablet Motrin
1 tablet as and when required
• Avoid strenuous activity & lifting heavy weights.
• Apply diclofenac
gel on the affected area. Warm compresses will also help.
I do hope that you have found something helpful and I will be glad to answer any further query.