Now 8 weeks 5 days: I started having light, brown spotting a week ago. Went to the ER on Saturday (third day of spotting) and had a blood test and ultrasound showing good levels and visible and nice and quick baby heartbeat, was advised all looked good and no need to worry. I was also advised that the ultrasound picked up a cyst on my left ovary which is a "probable hemorrhagic corpus luteum cyst," according to the ultrasound write-up. It seems the cyst hemorrhaging is probably the source of the spotting. 

Anyone know from experience how long this might go on? 

Nothing has changed (no new pain or increase in spotting or change of color) so I'm confident that we are still okay, but it is kind of weird. 

I can see how people who don't know they're pregnant might think they're having a period, with spotting going a whole week or more! 

Update: I did end up having a miscarriage within a week of my ER visit. No clue if it was because of the cyst or some other reason.