Black menstrual blood and stomach problems?

I am 16 years old. For the past year I have been going to the E.R. and doctor for stomach problems. When I eat, I can't hold my food down. I automatically throw it up or I have diarrhea five, six times a day. And it's very painful. I am always nauseous. There have been two times where I have been rushed to the E.R. because I had violent stomach pain. So bad to the point I couldn't move; it was crippling. The pain is where my stomach and left kidney is. Each time, the doctors have told me it's probably muscle pain or gas. But, I know my body well enough that it's definitely NOT that. About three times, my stool has been black. I have horrible, horrible stomach pain all day long. And I can no longer eat, I was 125 ibs. and now I'm 93 ibs. My pants are literally falling off me.
I have been taking birth control for a little over a year. My periods have ALWAYS been regular and normal, since I started having them at 12. For the past week, week and a half, I have been almost having my period. It's a little more than spotting. I am not scheduled to have my period until a few more days, so this is highly irregular. But my blood is black. And I'm worried.
Every time I see a doctor they always dismiss it. And I'm just wondering if anyone could help me out and possibly give me some insight into what this is.
I am NOT diabetic, I have no STDs, I do not have high blood pressure or cholesterol, nor do I have any blood problems.. I'm not anemic. I have had all my Gardasil shots. I am not sexually active. A few months ago, I had my white blood cell count checked, and it was normal. I don't have IBS or anything like that.

Someone, please help.

Oh.. I forgot to add, I have frequent, random nosebleeds.

You need to see a Dr. I would start with a Gastrointerologist and a scope of your bowels and intestines, you may have a tumor or cancer of the bowels. I had a friend who also could not keep food down when he ate and terrible pain. Turned out he had a hole in his bowels and a cancerous tumor. He got treatment and was fed through a feeding tube for several months but he is cancer free now. I hope this is not your case but it is better to get it checked out early. After that, if you don't have a gastrointestinal problem the Dr can refer you to a Dr who he thinks can help you. Good luck

I am a doctor, email me i need to know more but then i could try and diagnose u, POOR U SOUNDS NASTY.

sounds like old blood to me.. just call your gyno for an appointment.. i dont know about the stomach pain.. i hope you feel better

This sounds like you are really uncomfortable. You need someone to take a look inside you either with a barium series (which you drink) or with a colonscopy. Chances are very high that it is NOT cancer. I don't know why someone would put something that scary in their answer. It might be as simple as chronic appendicitis or an blockage from scar tissue or endometriosis. All are easy to fix with minor surgery.

You might want to start by going to a new doctor. It doesn't sound like your current doctor is really listening to you.

Good luck, I hope you feel better!