Heavy bleeding for 3 days

Glow had that I would start my period on the 22nd which would be correct. So as I was expecting my period to start soon I ended up waking up to heavy bleeding two days early on the 20th. It was heavy the whole day and continued on the 21st. On the 22nd the day I was really supposed to start I was still bleeding but no where near as heavy. I woke up the morning of the 23rd and was completely dry and still today no bleeding. I only bled for three days. I took a pregnancy test yesterday but it was negative. Anyone ever experienced this or know what it could be? I've been regular about 5-6 days and on time. But this time it was weird