Posture corrections must. Stretching exercises of spine and legs.

Get the chiropractic and osteopathy very common in first child

There could be two possibile reasons why you get such pain ( both of which are interrelated  but management is being slightly different) 1. Spinal origin pain in leg or radiculopathy, 2. Physiological changes during pregnancy. During pregnancy there's lots of internal changes in body, the most common being loosening of soft tissues like muscles and ligaments, which is because of release of hormone called relaxin which causes physiological weakening of muscle thus causing musclar pain, also another important factor is distension of tummy causing stretching of tummy muscles thus causing further loosening of tummy muscles or core muscles, as a result the support system from spine reduces and compression on nerve might cause pain in leg.