Is this normal?? Should I be concerned?? TMI WARNING

I’m on the pill...I don’t THINK I’m pregnant, but there’s always a chance I could be wrong. I just wanted a few opinions before I go out and buy a test. I had my period already this month, and it’s only been 2 weeks since then. I track my periods every month and the estimated period date is usually pretty much when I start. A few days ago I started having light bleeding then light-medium bleeding (enough to go through one tampon throughout the day.) My normal periods are usually very heavy, so this is quite odd. My cramping was very uncomfortable and causing some achey-ness in my lower back.