Long Term Strained Musces Pain

Over eight and a half years ago I developed pain in my chest, upper back and sides from doing regular heavy lifting. The pain was most noticeable when exerting myself. It would take hours after work for the pain to become tolerable. I still can't bend over for more than a couple minutes without getting chest pain. After about three years the pain went away mostly as long as I took it easy. Then about four years ago I was forced to do heavy lifting again and over the course of a few weeks the pain was back and worse. I've been trying to take it easy since but it hasn't gotten much better. Most doctors say its probably strained muscles and at best recommend physical therapy. Such therapy is expensive, from my brief sessions they gave me several stretches to perform daily but in the year I've been doing them it has had made little difference. I also have scoliosis but I doubt this significantly contributes to this. I have had several EKG's and chest/back x-rays done and they are normal. Is this strained muscles? Are there any methods to reduce the pain?