Implantation bleeding is a small amount of bleeding from when the baby (known at that point as a blastocyst) sticks into the womb lining.
Some people may notice a small amount of brown blood about the time their period is due or like me may actually thing their period has started, but find nothing there when they change the tampon (boy was I ever confused lmao).
7 weeks later is not implantation bleeding as this occurs approximately 2weeks after fertilisation.
There are a million and one reason as to why you may notice a little bit of bleeding at around 7 weeks and the only way to be 100% sure is to go see your doctor/ob/gyn