Implantation bleeding or just a weird period??

So I’m wondering if this is implantation bleeding or just an odd period. I was suppose to get my period tomorrow the 17th, but I started bleeding on the 12th. I thought hey, my period must have came early, although that doesn’t really happen to me, it’s more late than early. As soon as the bleeding happened I noticed and felt like something was off. It didn’t feel like a normal period. Now, I was experiencing cramps, really bad lower back pain and a little bit of dizziness, but I just brushed it off. I put a tampon in and just went on with my day. Day 2 of it and it was still really light, like really no need for a tampon. When I pulled the tampon out it was like a dark brown. Now at that moment, I was like this isn’t normal for me. Normally it’s super heavy day 2. Now fast forward to today. It’s day 5 and I’m barely bleeding. I only notice it when I press up. It’s like a watery pinkish red. At 1 moment I thought it was a little heavy, not heavy heavy but like a medium. but still not as heavy as it should be. The blood is like a light pink and some brown. Now, i’ve heard implantation bleeding can last for more than two days but I’m just not sure if this is implantation bleeding or just a really weird period. I did take a pregnancy test and it came back negative but I did read something today where it says you should take a test 2 to 3 days after the bleeding has stopped. What do y’all think and has this happened to you?