The exact solution is going to depend on several factors, including your other exercises and the type of pain you're getting.
Are you getting DOMS? If you are, then you're probably fine and just need to rest a day and suck it up in the later days. Stretch more, get plenty of water and protein, and get back out there.
Are your muscles spasming/cramping? If so, then you probably want to make sure you stretch more after your workouts and on off days, maybe do some more dynamic stretching, or more warming up, beforehand. You may also want to "deload" and do lower weight for the same number of reps and sets and work back up.
Is it not muscle pain? When you're "out of commission," do you get sharp pain down one of your legs? What does the pain feel like? Where is the source of the pain located? If it falls under the "not muscle pain/DOMS", then you probably want to see a doctor. Lower back pain and sharp pain down a leg is a sign of Sciatica, where the Sciatic nerve gets pinched. Even if it's not Sciatica, if it's not muscle pain, you don't want to injure yourself further. Get checked out and make sure everything is okay.
For any of these, and everyday activities, make sure your posture and form are correct. When standing straight, your spine should make a gentle S-shaped curve. Your skull should sit comfortably on top, your hips in a neutral position at the bottom, your shoulders back some, and your ribcage up and out of your hips. Your shoulders and hips should be parallel to each other and the ground, and your weight distributed evenly between your feet. When working out, make sure your back is as straight as the exercise allows (ie - when doing things like squats or deadlifts, the back shouldn't be rounded - the form should come from bends at the waist/hips, knees, and the other joints involved).
Also, make sure you don't overwork your back. Just like you take rest days between the other muscle groups you work, your back needs rest. Remember, too, that if you're doing compound lifts, you may be working your back, already, so make sure to count them, as well, when determining how much you've done.