What is this????

Help me 😭 my period was 16 days late, I took a few pregnancy tests but I wasn’t really worried as I just got the Nexplanon implant the day I was supposed to start my period. I started spotting on Thursday so I thought, oh it’s just my period And it’s super light. Today it got heavier though and just now when changing my tampon, I found this. Should I be worried?