bleeding at 15 weeks?

Sooo Im pregnant with 3 and started bleeding Sunday... so the doc told me to stay off my feet the rest of Sunday and monday..so I did, but it didn't stop. he sent me to get an ultrasound at the hospital yesterday. today, i got a call from him and told me i need to stay home from work until friday and that it wasnt my uterus bleeding...I'm still bleeding. so I'm worried even though my doctor said it should stop by itself as long as I stay off my feet, and it sounds dumb to not listen to the doctor but it drives me nuts not knowing where this blood is coming from!! has anyone else randomly bled? and were you told where it was coming from?