An ER will not do anything to help, and you aren't suffering from an emergency, even though I know you are miserable with this. It's been a long hard road and the bad news is that it's probably going to be miserable for a while longer - diagnosing GI problems is not simple, and you will be put through a few tests, and some waiting, before you get to feeling better.
The good news is that you already have an appointment with a GI. It's a week away, though, and since you are losing weight and unable to work or go to school, it is worthwhile to call the GI's office and ask them to push up your appt. Tell the nurse or appointment desk or whomever that you are really suffering and need an earlier appointment. They should be able to find a time to see you in the next day or so.
Your DR should schedule you for some blood tests and ask you to collect stool samples. The white strings you are seeing are mucous. Please be prepared to answer all of your DR's questions, and to explain IN DETAIL what is going on. Bring a printout of this forum post and make sure s/he reads it. Part of the problem with bowel issues is that they are unpleasant to talk about, and everyone feels embarrassed at first. But trust me, your GI has heard it all and expects to discuss these things, so please do not be shy. That will just make diagnosis more difficult.
Best wishes, and I hope you feel better soon. And come see us on the Crohn's or Ulcerative Colitis board when you have questions after this appt.