Can home pregnancy test results change?

Megan • Happily married since 9/29/13
I took a home pregnancy test early this morning, only 1 line showed up (not pregnant) within a minute or so. I threw it in the trash. For some reason a few hours later I had the urge to look at it and it is positive. We've been trying fo so long and I don't want to get my hopes up if I'm really not pregnant. Can they change if they sit too long???