My placenta is not low (it is in the front, but high enough up, apparently).

The ob said that as long as I don't have any more bleeding (and I haven't had, other than those 3 drops on the sheet Saturday night), it's not a worry. Especially since baby's heartbeat was fine today and she's moving about. So that's alright, I guess.

I'm really mostly relieved to have not had more bleeding than by what the ob said, but it was nice that she said firstly not to worry and then told me when it would be reasonable to worry (if I had more bleeding, if I had cramps, if I lost amniotic fluid).

I suspect it really was the amount of walking I did on Saturday that might have overstressed my body a bit, so I'll try to take it easier this week, and hopefully no more scary things will happen.

Thanks for your good wishes, everyone.