Paracetamol is helpful. Also you can go for hot bag fomentation. Do check your mattress. Not too hard not too soft. Should be firm. Take rest by lying in the bed and pillow below the knees so that the knees are bent. Avoid sitting on floor, forward bending, lifting weights, while sitting take complete support of the backrest of the chair. Yes back extension exercises will be helpful. You can contact either your obstetrician or orthopaedician for this.

You can contact your nearby pain management clinic. Avoid strong pain killers in pregnancy. You can give some hot packs on back as pain is coming from her back as per your description.

This mostly due to disc disease. As in pregnancy due to postural changes it puts abnormal stresses on spine and thus the symptoms progresses. Take paracetamol tablet upto 3 times daily Apply ice packs Avoid forward bending, lifting weights, prolonged sitting posture Do spinal extension and sciatic nerve stretches available at YouTube Use hard mattress Apply diclofenac and muscle relaxant gel locally twice or thrice Avoid tens