Thanks for writing to us.
From description , it seems you might developed muscular or ligamentous strain over back .Lump most likely to be due to muscle spasm.
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 anti-inflammatory gel on the affected area
Hope this helps you.You can consult me again directly through my profile http://www.healthcaremagic.com/doctors/dr-saurabh-gupta/64132