Yellow discharge from an incision can be normal. However, this could be a sign of an abnormal process. I would strongly encourage you to talk to and see your OB / GYN or surgeon
who performed the procedure.
Discharge from a fresh incision can be normal. In general, there is fluid that bathes the tissues, and this can occasionally leak out of the incision and therefore cause minimal drainage. This is usually clear or yellow. It is not often foul smelling. In fact, the foul smell can be a sign of a specific type of bacterial infection (anaerobic infection). So your discharge could have been normal early on. Regardless, after 7-14 days, an incision should have healed. Normally the surgeon will not remove the staples or sutures until the incision looks fairly well healed. After that, there should be little to no discharge from the incision. If there is excess discharge -- possibly from a problem with a deeper layer in the belly that was likely closed -- this requires evaluation.
All together, this could be a sign of infection of the wound. I would see your surgeon to discuss this.
Another possibility is an infection of the skin fold (on the skin itself). Keeping the area dry and clean is important. This is also a concern as bacteria may then enter the wound.
See your surgeon. This is concerning for an infection.