Implantation Bleeding?

Hi all! I'm somewhere between 4 and 6 weeks along (extrapolating from my typical cycle + a positive pregnancy test), and I've had brown spotting (VERY light) for around 3.5 days.

Is this normal??? This is mine and my husband's first pregnancy and it's rather unexpected. I would ask a doctor but we haven't been able to afford insurance. We are hoping and praying that a new upcoming job opportunity for my husband would remedy that, but that's still some time off, and I would greatly appreciate some peace of mind in the meantime.