Hello, Increase in weight gain increases the load on the back which may increase the pain. Advisable to visit a physiotherapist who can assess you and know the exact reason of pain.you make sure you maintain good posture .bad postural alignment can also cause pain. Avoid long distance travel ,lifting heavy objects and always turn on one side and get up from  bed . Regular exercise, walks or pilates or yoga is must ! You may take heat pack to releive pain .