Major TMI ALERT

Hello! So this cycle my period was unusual and google has been no help
My period started on Monday (Nov 5) with very mild cramps and mostly brown light flow. It wasn’t due until Tuesday so it started a day early. Then light/medium flow in Tuesday and Wednesday with no cramping. This is already unusual for me because I always cramp a lot with heavy flow for several days. Wednesday evening I also had an odd sharp ‘pop’ feeling on my left lower abdomen with a dull ache following for about and hour then the pain vanished. I woke up Thursday to a almost dry tampon so I put on a panty liner and went about my day. Thursday afternoon I was suddenly hit with killer cramps and about 2 hours of extremely heavy bright red blood. The pain subsided with the help of Tylenol and by evening my period was almost gone again. Now today (Friday) it’s down to dark red/dark brown spotting occasionally. Any suggestions what was going on with the bout of painful cramps/sudden heavy flow Thursday ?