Vaginal Bleeding with no cramping

I'm 15 weeks pregnant and had some vaginal bleeding without any pain or cramping.  I went to the ER and the ER doc ordered a ultrasound, blood work, and did a pelvic exam.  The vaginal bleeding lasted at most an hour and a half.  The result of my ultrasound was that I have a low lying placenta and the baby was not in distress at all.  My placenta was not low enough to diagnose me as having placenta previa as no part of my cervix is actually covered.  When the doctor took a look she stated there was a clot coming.  I was then released.  When I went home to shower, a small clot came out.  I did follow up with my regular OB the next day and she took another look and saw a clot as well.  I didn't think to ask her if it could have been the same clot and only a small piece broke off.  It's been two days and the clot that my OB saw has not come out.  Should I be worried?  My OB did mention the placenta could be trying to detach itself.  I think she was just trying to prepare me for the worst case scenario.  What are the chances of the placenta detaching when I'm not bleeding or in any pain?  Could the clot be stuck in my cervix?  If that's a possibility, could that be stopping blood from flowing out?  I have an appointment with my OB on Monday and plan on asking her the same questions.  Are these legitimate questions or I'm I freaking out a bit?

[RNwant2bmom]

I would go to ER. Sweetie, it sounds like a  placental detachment.

[California_Margarita]

No placental detachment.  Just a low lying placenta.  Apparently the dr was just making me aware of the worst case scenario.  I told her she scared the crap outta me.  She checked the baby's heartbeat again.  The baby is still doing great!