What Causes Tissue Discharge During Periods?

hi, I am a 22 year old woman that started seasonique extend birth control pill this past march I just received my period for the first time since starting the pill, and today I noticed that a piece of skin or jelly like substance that kinda looked like a piece of liver came out during my period and I’ve been really crampy. I’ve never had this happen before so I’m a little concerned. I am sexually active and we typically use condoms but there have been times we didn’t.