In-between bleeding but now period is late. IUD

I have the non hormonal IUD. I had in-between bleeding 10 days after my period that last a 1-2 days. I often have spotting in-between periods because of the IUD but this was like fill up a tampon almost and lasted longer than a day I thought my period started early. Then it stopped suddenly so I assumed it was no my period because they generally last 7 days now. But now my period is 3 days late which is uncommon. Any ideas? I took a pregnancy test a couple of days after the bleeding stopped because it was weird but it was negative. Could that have been my period ?