B.D.
My daughter went through the same not long ago. We found out that it was a combination of an ear infection and teething. It really could be a number of things. If things don't improve soon it may be worth mentioning to her doctor.
Good luck and hang in there....I know it can be tough!
To add on: I see someone else mentioned reflux...my daughter also had reflux and had to sleep propped up for a while. It very well could cause her to wake and scream like that. My daughter grew out of reflux by 12 months old (she had it from birth) it is worth mentioning if you seek medical advice about this. :-)