Help! Faulty test?

Megan
So I took a test yesterday and the line was faint, but it was there. Took my pictures and such, and then about 20 minutes later the line was gone. Tested with fmu today and it was negative. I know tests are invalid after certain amount of time, but I always see people's positives sticking around! Was my first test just faulty? Any ideas? 10dpo