I'm so sorry that you suffer from chronic pain. The best solution I can give you is to find a specialist in pain management. These people are trained to know when people are in genuine pain and when they're just doctor shopping. Since you've been on pain medication for several years, it stands to reason that you need an increased dosage. A good doctor will recognize that and help you through your pain.
Social Security Disability can take years to get, but it is worth applying if you believe that you may be out of work for at least 1 year. I'm over a year into the process now and am hoping to get my benefits sometime this year.
I hope things work out for you and that you get relief from your pain and your financial difficulties!