The key difference between polymyositis and fibromyalgia is that the polymyositis has true inflammation in the muscles, whereas in fibromyalgia, there is no inflammation. Both affect the muscles and cause pain that is felt in the muscles. The polymyositis usually causes weakness more than does the fibromyalgia. The fibromyalgia can develop in someone with another inflammatory condition, but there is no inflammation present from the fibromyalgia, which is why the old term for the condition, fibrositis, is not typically used.
The inflammation of the polymyositis is what causes the elevated CPK, which is typically normal in persons with fibromyalgia. Although it is theoretically possible that the fibromyalgia could develop in someone with polymyositis, it would be impossible to make the diagnosis, as the hallmark of fibromyalgia (tender points in muscles) can occur with the polymyositis. If the treatment for polymyositis leads to improvement in other measures of disease, such as the elevated CPK, but the muscle tenderness persists, then there may need to be consideration of whether fibromyalgia also is present.
The usual first-line treatment for polymyositis is steroids, such as the methylprednisolone. The methotrexate is the usual second medicine to be used. It is true that adding a non-steroidal anti-inflammatory medicine to a steroid is generally unwise, because of possible side effects. Using Tylenol is OK, as it works by a different mechanism. Tramadol is also OK, although you had a reaction to it. If the Tylenol is not effective, then the usual approach would be to use a pain medicine, such as codeine or hydrocodone.
These medicines have been studied in a wide variety of chronic pain syndromes, and appear to help with chronic pain by decreasing the firing of the nerves carrying the pain message. These medicines are not typically used for polymyositis, because the other interventions are usually fairly good are controlling the condition, so managing chronic pain is usually not much of an issue. However, if you are allergic to opiates, then it would be appropriate to consider using one of these agents.