I also suffer with 3-7 day migraines. I wanted to let you know what I've done in the past to stop the pain. I realize this may or may not work for you, however I hope it will help you in some way.
I go to the ER when I can't stand the pain anymore. I go to a migraine clinic at the hospital where I live and they give me an IV called a cocktail. Anytime I've been out of town and had to go to another hospital, they try to take the pain down with just Demerol and other drugs, but they don't work, of course. All ER docs know about the cocktail (a mix of drugs that treat all symptoms) but rarely offer it unless asked. Show them that you know what you're talking about and that you won't accept anything less. Sometimes it helps to take someone with you who is strong and willing to be pleasant but assertive to make sure you get what you need...and don't leave the hospital until you're better.
Regarding the worry about asking for drugs...don't worry about it, only care about yourself. I had a nurse ask me one time what my pain level was on a scale from 1-10. I said I thought about a 9. He replied with "uhhh ...a 10 is a person who has been lit on fire, I don't think you're a 9!" That is ignorance talking. People with migraines have to deal with it often, but you can't let it stop you from seeking treatment.
Take care. My heart goes out to you and I wish you the best.