Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
There is a material that cushions the space occurring between the vertebra (bones of the spine). This material may sort of be squished out from in between the two bones; this is called a herniated disc. With time, the amount of disk that has herniated shrinks and with time resolves completely in most people. Therefore, a recurrence of symptoms year later, in the setting of activity such as years (unloading building materials) may signify a new herniated disc. This can lead to a pinched nerve, or radiculopathy. The alternative though is what is termed paraspinal muscle spasm, or basically muscle strain in the muscles on either side of the spinal column.
Regardless of whether it is a herniated disc or muscle strain, unless there is weakness, sensory loss, or bowel or bladder symptoms, treatment would be conservative (non-surgical). This treatment may include medications (non-steroidals such as advil), sometimes steroids if there is swelling (edema), temperature therapy (hot or cold packs), stretching and controlled physical therapy, muslce relaxants, and so on, these are best prescribed by an experienced physician, each has its own indications. I can not make specific treatment recommendations, and recommend you see a primary doctor/internist. After he she examines you, he/she based on physical examination can assess whether further testing is indicated, such as an MRI of the spine.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
A related discussion, about ribs was started.