Positive and Negative Test

I have taken a lined first response test this first thing this am and it showed faint positive. Later this am I took a clear blue digital and it showed not pregnant. For reference, I took several test the last two days and they showed positive, including the same type of digital test which showed positive. I have had very minimal spotting for about 6 days prior to my expected period. Still have some minimal spotting now. Called the OB and they don’t seem to worried, said check again in a few days. Anybody have anything similar and still turn out to be healthy pregnancy?