when your back gets tight like that its likely due to muscle spasms. next time it feels tight try taking lots of magnesium citrate. dissolve it in juice. take up to bowel tolerance, in other words take as much as you can without it giving you the runs. the magnesium helps to relax the muscles and loosen up the spasms. juice fasting also helps with plenty of green juices as they are high in natural magnesium.
as for chronically sore muscles its possible you have a clogged liver, or maybe mercury toxicity due to Amalgam poisoning.