Brown blood is old blood. It's probably just spotting which is very normal for early pregnancies.
Implantation bleeding happens 4 to 7 days before you miss your period so it is not implantation bleeding you are having yes sometimes spotting can be normal and nothing is wrong but it can also be a sign of a complication I had brown spotting with my first pregnancy and I miscarried so I would get checked out its always better to be safe than sorry