Should I retest later?

Ok so I took a pregnancy test this morning. I was watching the window as I always do and I seen the first line (indicating a positive result) a faintly. It wasn't to faint to wonder if it was really there though it was dark enough to see and know it was a line but as everything moved down the window the line disappeard only to show the second line (indicating a negative...again). We've been trying for a while and I am seriously starting to lose hope and have started thinking about adoption more here lately since I had decided that if I can't have kids I would adopt. Should I retest later or is the test more than likely negative even though the two lines both appeared but then the one disappeard? Help!! I've never seen a test do that and we've been trying a little over a year. Any input would be appreciated.