Probably you are using gns3 for the fist time and getting this problem! that when you make you topology, make all configurations, save it and when you restart the gns3 all the configurations are gone away, and only the topology diagram is there?
Don't worry it is because you are missing one step while saving your Router's configurations in gns3, that is you have to export the configurations after that you have to save the gns3 file.
2. Click the FILE menu and Click Save.
Step are also shown in the Snap below, Please click to maximize it.