Cymbalta belongs to a class of drugs called SSNRIs - selective serotonin and norepinephrine reuptake inhibitors. It acts by affecting two chemicals that occur naturally in your brain and spinal cord, serotonin and norepinephrine. Cymbalta is prescribed for major depression associated with physical symptoms like pain. It is also prescribed for diabetic peripheral neuropathy. Although it might make you sleepy, it is not a sedative or tranquilizer but an antidepressant. It does help the physical symptoms associated with depression, but it isn't intended as a pain medication. Cymbalta is a prescription only medication.
Soma is a very strong muscle relaxer - it's generally prescribed for short-term use for the pain and stiffness associated with a sprain or strain. It makes some people very drowsy - you should not combine it with alcohol, antidepressants or sleep medicines.
If you are having difficulty sleeping because of pain, you should talk to your doctor about the right medicines to help. Cymbalta and Soma aren't for everyone - they have side effects like most medicines.