This one is a back breaker! But don't worry; I have some tips that would prevent your back pain from worsening. A workout session in the initial stages of pregnancy stretches your back and leg muscles, and strengthens them. It alleviates back pain greatly.

Believe me, swimming works! It worked for me. It strengthens your lower back. The buoyancy of water relieves the strain from your joints and ligaments.

ALWAYS SIT STRAIGHT TO AVOID BACK PAIN. If you work on computer for long hours, take a short break every hour and move around. It stretches your muscles and relieves pain. While sitting at the desk, keep your feet a bit raised from the floor.
 
Shoes play an important role in pregnancy. Get a comfortable pair for yourself. So, forget those pointed 6" inch heels for certain period of time. As soon as you get home, take off your shoes and let your feet free.

WHEN YOU NEED TO LIFT OBJECTS, ALWAYS BEND FROM YOUR KNEES AND NOT FROM YOUR WAIST. This saves your back from an injury.