Bfp then bfn

Hi guys, this morning I posted a bfp and everyone was able to see it even though it was faint. I ran errands all day and held my urine for 6 hours. Grabbed a frer when I got back to see if the line got darker and to my surprise it was blank. I haven’t drank anything all day so it couldn’t be diluted and I am so heartbroken right now and don’t know if something is wrong with me or if this has happened before and someone miraculously still ended up pregnant 😭😭😭