I'm at my wits end with my 17 month DD.
Having previously been a good sleeper we have descended into sleep Russian roulette where she will either sleep through the night or wake between 2/3 and be awake for at least 2 hours if not longer. Last night she woke at 2.30 and wouldn't go back to sleep until 5.30. 
This has been going on for 2 months now and I'm at the end of my tether. She washes up crying and will immediately lie down once I go in. But as soon as I leave she screams again. She won't sleep in our bed just climbs all over me and if I stay until she goes back to sleep she wakes up 20 mins later screaming again.
What can I do? It's so frustrating because at least once a week she does sleep though so I know she can do it. She's so tired and miserable in the daytime it makes me so sad.