Your problem is common in persons with a history of low back pain
. When you get pregnant, you tend to bend backward to compensate the abdominal bulge forward. This posture is called hyperextension, and that puts pressure on your low back. This condition can be managed effectively with application of some ayurvedic oils on the back and mild back exercises. You can also consult with qualified Ayurvedic physicians who can advise safe and mild herbal preparations to help with teh back pain. The problem will definitely be managable and will clear completely after child bearing.