Is there any overlapping of the skin where your scar is? If you have a skin crease there, you probably have a yeast infection in the crease. If you have a crease, you may want to try a topical antifungal.
My c section scar is only just less then 2 years old, so I cannot say that I share this experience. However, I would probably see your Dr. It sounds like this should be investigated. All the best to you.