help needed!

Bethany • Baby no.1 born 29/05/19 🩷 Baby no.2 born 10/12/23 🩵 Baby no.3 due October 2024
So, I've been off my AF but for about a week now I have been cramping and at the beginning I had some light brownish bleeding for a few days on and off. I took a test and it was negative but my AF isn't till next week. 
Any ideas on what on earth is happening. I thought implantation bleeding but??? 
Actually my last AF was the 29th of August