Faint positive yesterday, negative today?

Iulia
Did this happened to you? I did a hpt yeasterday and I saw a faint line in the correct time frame. I reporters the test today (not first urine) and it is BFN.
I don't have any spotting or bleeding, no bad cramps or any other alarming symptom. Could've been a false positive? 
I am 4 days before period today. 
Thanks for replying!