Mama: Are you seeing house sparrows nesting in the house? They are aggressive non-native species and they will take up residence in your martin house. I would post this on the bluebird forum. Many members have martins and would know whether they are in your area or not yet.

The attached link has scout reports for South Carolina. ("scouts" refers to martins returning in the spring looking for nesting spots.) There are probaby martins near you, be patient. You may want to try putting out gourd houses as well.

Here is a link that might be useful: martin scout report, south carolina