I have discomfort with my back in the middle either side of the spine,i over stretched i think with a weight and now feels like a lot of pressure&pain?

Muscle strain: As long as you are not experiencing symptoms into the legs (numbness/tingling), your localized back pain is most likely due muscle strain. As a general treatment strategy: application of ice, and consider wearing a simple back support for a few days. If able, NSAID treatment for a few days can reduce inflammation and pain. If symptoms persist a visit to your doctor would be advised.