10 weeks drop of blood

I'm 10+4. Had my first ultrasound last week and heard a heartbeat of 174. Sorry for TMI- but just when I went to the bathroom I had a small drop of blood in my underwear. Not bright read but more than brown. No bleeding at all thus far and no period like cramps. Mostly just muscle stretching now and then that I can tell. Has anyone else experienced this? Making me nervous of course!