I would try not to worry unless you are in pain or otherwise feeling unwell. Something that tiny could have come from anywhere. When you have bleeding that you need to be concerned about, you'll know it because there's usually a lot of it. I had some spotting at 16 weeks as well (I also had a heavy bleed at 10 weeks) and all was fine. I did go for a scan after the heavy bleeding (it was like blood gushing out of me though), but I didn't even tell my midwife about the later spotting because it didn't seem unusual or abnormal. If it gets heavier, I'd give your OB or midwife a call and ask them what they would advise you to do, but I'd avoid the hospital if you can unless they send you there. If you've had no more since then, it's probably just a little irritation from your cervix and it would probably be worse to spend a day in the ER surrounded by lots of sick people than it would be just to rest at home.