Your symptoms certainly sound like early pregnancy, and it's definitely not unheard of to get a positive on one pregnancy test and a negative on another because of variables like what time of day you took it, how sensitive the test is, etc.
If the first one you took was clearly positive then I would ignore the ClearBlue and try a different brand to see what it says. I've encountered false positives on cheap tests before, but they were light. If the second line was very bright, then I would consider that negative.
So, if you haven't already, go out and grab another pregnancy test (not ClearBlue) and try again now that your period is late.