Has this happened to anyone else?

Hello Iv been on the birth control pills for the past 9 months ... I started what I thought was the start of my period on Tuesday dec 10th ( which was a day late) and it started off super light almost like spotting then got a little stronger ( not much) were it actually got some on my tampon after 5 hours but then got light again and only lasted about 3 days ... I have had slight cramping but nothing major or how it usually is ... what can this mean? ... I’m usually a very heavy bleeder where I fill a tampon with in 2 to 3 hours and that usually last 5 days and I am just wondering what could be going on? And should I call my dr? Or should I take a pregnancy test? Iv Never had something like this happen so I’m not sure what to do

Thank you in advance for the help