What could this be?

I'm 16 weeks 2 days today and when I just wiped I had a teeny tiny streak of blood in my cervical mucus. The same thing happened to me last Tuesday. It's not a lot of blood at all and someone else who wasn't paying close attention probably wouldn't have noticed it at all. Both times it was inside the cervical mucus which I've had a lot of this pregnancy. I checked the heartbeat on my home Doppler after it happened and everything sounds normal. I've also felt a good bit of movement today so I know the baby is ok. What could this tiny amount of blood be? I don't have another appointment for 3 weeks so should I just wait or is that small amount of blood worth mentioning before 3 weeks from now?