When working on a research project, save yourself a lot of time and aggravation with one simple step. Keep track of your research trail. What is a research trail? Think back to the story of Hansel and Gretel, and those pebbles they dropped on the ground to find the way back home.
Instead of pebbles, make notes, either on your computer or in a notebook, of the sources you have searched. And also keep track of the search terms you have used. This trail or log will make sure you do not repeat the same searches, and also, if you meet with a librarian or your professor for a research consultation, you can show exactly what you have completed, and the sources you have already located. The trail notes can also help build your bibliography and footnotes later, when you are drafting your paper.
So, save yourself time, and be sure to make a trail of your research!