Thanks for your query.
From description , it seems he might developed muscular or ligamentous strain over back .
Meanwhile following measures will help with the pain
• Lie on a hard bed.
• Anti -inflammatory drugs like Tablet Motrin
1 tablet as and when required
• Avoid forward bending.
• 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.