If you go to the ER, they are more than likely going to take several vials of blood, pelvic exam and possibly an u/s however only being 4wks they won't be able to really see anything except the endometrial lining.
It might be worth your wait for your doctor tomorrow, because he/she will know more about you and have a better treatment or testing plan.
Unless you are starting to be in allot of pain, cramping, fever, allot of bleeding then I would wait... tomorrow is almost here

I'm SO SORRY you feel like things are up in the air!!!