Sounds like a very good selection of foods. Just to be sure, you offered the Nyjer in a Nyjer feeder and the sunflower in a sunflower feeder? The ports are different. Otherwise, patience is the key. You might also add water. The sound of running water is a big attraction to birds.
This web site has lots of good info on purple martins.http://purplemartin.org/
There must be a lot of free flying space around the martin house. Martins will not come if there are too many nearby trees. If you are purchasing a new martin house, make sure the pole design makes it easy to raise and lower the house. Until the martins are established, the odds a very good that you will have to remove House Sparrow nests on multiple occasions. If you leave the House Sparrow nests in place, it is unlikely the Martins will try to move in.
The timing of opening your martin house is also important. February is not that far away, and martin scouts could start arriving in your area in late February. The web site mentioned has a map of arrival dates.