How incredibly scary! If they say they have checked all they can check in the ER, I don't know what else you can do. Does your dr. have an answering service where you could at least speak with your dr.? That way, they'd know what is going on and get you in first thing Monday.
As I read your post, I immediately thought about an AngelCare Monitor if you do not already have one. I cannot understand why doctors don't tell us about these! It will sound an alarm if she doesn't breathe for 20 seconds and has a setting where it will tick every time she takes a breath. I have used it the last 2 kids and will use it with our next baby. (My firstborn stopped breathing at 6 months due to RSV.) I bought mine on Ebay for $30 including shipping. I have found them for friends for about the same price. (They are $100 new.) You might get lucky and find one on Craigslist, too.
My only other thoughts...has she had any upper respiratory infection lately that has worn her little lungs out? (Of course, that much crying could wear her out!) Are you giving gas drops? If she cannot tolerate formulas, have you considered trying to get breast milk from a milk bank. Check Le Leche League. Although she might not be throwing this one up, it still can be causing discomfort. A friend of mine donated milk to a little girl who couldn't tolerate any formula. The breast milk worked very well with her. Good luck! Praying you get help soon!
J.
Mom to Jackson, Keaton, Landon...and baby #4 due 2010.