TMI implantation or period?

So.... AF was supposed to arrive Friday 6/19, but hasn't arrived. My periods are almost never late, so I've tested with FMU the last three mornings in a row. All bfn :( I put in my menstrual cup this morning just in case AF made a surprise visit and when I checked this afternoon there was the smallest bit of what looks like a blood clot to me and nothing since. My cycles normally start like Niagara, so I'm wondering if this could be implantation bleeding or not. From what I've read it's too dark. Other opinions would be greatly appreciated. Thanks!!