Missed periods but not pregnant?

maggie • 21 year old mama bear 🐻 girl mom 🥰 married to my high school sweetheart 😘 baby girl #3 due April 2021 🌸

Hi mommies, so here is my concern.... the last period I had was March 12, 2018 and it ended on March 18, 2018. Before all of that my last period was October 9, 2017 (ended on October 13, 2017). Well the period I had in March was SUPER BLOODY. The bloodiest period I’ve ever had & had huge clots in it. I thought maybe it was a miscarriage.... well now I’ve been late for my period for about 85 days (almost 4 months) took a pregnancy test earlier and it said negative but I have every sign of pregnancy... but I’ve also been told it could be a cyst or tumor in my uterus.... has this happened to anyone before? And what was it 😔