I'm only recently recovering from serious, long-term back problems, and I hope I can save you some time here. First, your muscles might just be in spasm, which is to say, clenching and not letting go. If this is true, you need to get them to relax, and certainly shouldn't make them stronger. Poke around down there: do you have two clenched sets of spinor erectae muscles even while lying down? Lower back spasm is very common, but can be tricky to treat. I had good success using the Somatics
method, and if you're in Denver or Cali you can find someone who does NeuroEnergetic Release, or NER.
Also may be disc problems. An MRI is good but not definitive, as any doctor who doesn't suck will tell you. I would try to fix the muscles first via the above methods before worrying too much about disc degeneration, unless you're having pain going down the legs.
Actually, you know what? I'm over-doing this. What sort of pain are you having, and when? Is it crippling, or just annoying?