Hello and welcome to health care magic. There can be different reasons that can cause pain from around an old surgical suture. One is herniation of underlying fascia and structures through a small gap that have occurred through the suture line. This is common in c section scars. Another reason is suture separation due to fatty and lax abdomen. This can result in development of secondary bacterial infections. So your doctor has rightly advised to do an ultrasound to understand the present condition of the scar and the possible cause of pain. Hope this discussion will be helpful to you. Thank you.