What is going on?

I’m thinking that I ovulated on August 26, but my app says I did the 29. Either way, I would be around 7-10 dpo today. My cycles are always 31 days and I never start early. But today I started having light spotting around 12pm, and it got heavier and heavier and the cramps got worse. At first it was only when I wiped and then it started getting worse and I had to put a tampon in. I have NEVER started a week early, so what could cause this? I don’t think it’s implantation bleeding because it seems too heavy? But I have been having all kinds of pregnancy symptoms lately. (horrible nausea and migraines which is very rare for me) I never get nauseous for no reason, but this is the 4th day that I have been nauseous and have had a horrible migraine. I’m also super tired and my boobs and nipples are incredibly sore. I took a test on Saturday and it was a bfn. What’s going on? 😕