Treatment of pain is in fact covered by insurance. However, you need your treating doctor to fill out a set of forms for the says that the pain is directly caused by the illness, is treatable, and is temporary. So medication for pain from illness and injury are covered, but cronic pain (like arthritis or carpal tunnel) is not.

Your doctor should have explained all of this to you before writing the perscription, at the very least telling you what would and would not be covered.

Pain is only cosmetic when it doesn't have a definable cause or solution.