At around 5 weeks I had a bit of dark brown discharge too, kind of like old coffee grounds. My midwife said it was likely just old blood from implantation or my last cycle making its way out. Since you don't have cramps and your tests are positive, it's usually not a big deal. Many of us have little bits of spotting early on. Just take it easy, avoid heavy lifting and keep taking your meds. If it turns bright red or you start having pain, call your doctor for peace of mind, but a bit of brown discharge is super common.