16 weeks and heavy bleeding***UPDATE***

Gabby
Just got home from the ER after having some heavy bleeding, toilet water turned red and toilet paper was soaked with blood!  Did an ultrasound at ER and babies (pregnant with twins) are fine, strong heartbeats, measuring a week ahead, moving around a lot! They couldn't find a source for the bleed and told me to make an appointment with OB first thing Monday.  I am still bleeding not gushing blood but red blood when I wipe and some blood on pad.  Anyone have something similar happened? What was the outcome or reason for blood? Any advice welcome! 
***update***
I saw my OB today and she did another ultrasound and thankfully babies are still doing great! She said because they didn't see any cause on the ultrasound they don't know why I bled, and that sometimes they never know.  She said heavy bleeding can be normal, especially with twin pregnancies.  Could have been a popped blood vessel in placenta or piece of placenta fell off, but either of those things she said not to worry the placenta will heal.  She said to expect to bleed brown blood for another week or two, but that it's good because it means the blood is leaving my body! Hoping this is the end of all this bleeding fiasco!