I am 6weeks pregnant and my lower back hurt bad when im at work, why is this?

Lots of Reasons: When pregnant, there are so many things going on. Your hormones are very different causing your ligaments to stretch quite a bit especially in the pelvis resulting in pain. Also the baby's position can place stress on your spine resulting in bulging discs or even herniated disks causing the sciatica pain. Recommend seeing a pregnancy specialized therapist that can guide you through this.

Pregnancy/back pain: Back pain is common with pregnancy. There is a rapid and significant change in hormones in the first trimester that can lead to changes in the tension or laxity of the muscles and tendons of the pelvis. Do exercises to strengthen the back and stomach muscles. Make sure that your chair and table/computer set up are ergonomically correct and not the cause of the pain.