Brown Dishcarge

I’m 4w3d pregnant and have been spotting brown discharge on and off every day for about a week. It hasn’t seemed to get any heavier though. I’ve had my hcg checked 3 times so far and the number were 216, 611, and 1,281. So seems like my numbers are going over double in 48 hours. I called my OB and she isn’t worried unless it gets heavier or turns red. Just worried because my last pregnancy ended in a miscarriage. Has anyone experienced this before and had a successful pregnancy?