I understand your frustration totally as we went through the same thing w/our DD who is also 19 mo's now. Slept straight through the night for many months fine, then all of a sudden out of the blue- refused to sleep in her crib, screaming and waking up to 6 X's a night.
Let me start off by saying that it will pass. Just as fast as it came on, she went back to sleeping straight through the night again after about 4 mo's. I know this is a long time to be exhausted so here's some advice i hope will help and what we did.
First we made sure nothing else was wrong with her medically, got her checked out. When she was first born she had GERD so we wanted to make sure she wasn't having any stomach or digestion issues that may have felt worse when laying down. Once we ruled that out, we would make sure of all the basics things- was she hungry? diaper, room at right temp? , etc. etc. When all these issues were ruled out, we did a very gentle method of sleep training making sure that we started only at a time when nothing major was going on, no new transitions that may cause her stress, no illness, etc.
We put her in her crib after normal bedtime routine of bath, then bottle, brush teeth. She would be very sleepy but not asleep. Of course she would cry. I'd leave the room and close the door and listen on monitor. I'd time it for every 5 mins at the most- go back in - not picking her up out of the crib- soothe and rub her back (she would stand up) and I'd gently put her back down and put her blanket on her. We did this for upwards of about 30 mins at the most and after 3 days - it got much better. Instead of waking 6 X's it was maybe 2-3 times. Also - we didn't think of it too much but her fave animal in the world is a duck. someone got us a pillow pet duck and we put it in her crib- that same night, she slept through the night for the first time in months!
During this period of non-sleep - if it was the middle of the night- we would also bring her in bed with us to sleep, that worked out b/c we could all sleep for longer stretches of time. We didn't do this a lot but occasionally we would. She wasn't confused by us doing a very gentle sleep training combined with bringing her into our bed occasionally. It really worked and now she sleeps fine.
I also believe that TEETHING was a big part of the problem. They can feel the discomfort even before you can visibly see that they are cutting teeth. We kept a frozen teething ring in the freezer and during the night wakings would let her suck on it for as long as she wanted to get some relief.
Sorry you are going through this- I know how hard it is.