Period only came on for a day already disappearing ??

The first two days were spotting so little I didn't have to put on a pad, yesterday was a full on bleed, but only for an hour or so maybe and then I was moving around and changed my pad twice. Noticed it lessened already ???

And then I took out my tampon after having it in for 5 hours and it wasn't full. I changed to a pad and no Flo just spotting. I took a pregnancy test on the 31st it was negative:( what could be going on ??? I usually have full 7 day periods, 5 days the very least.