3 year old screaming at night?? Help?

My dd was always a great sleeper and for no apparent reason just started getting back out of her bed and screaming at her stairgate for one of us. Every time I go up she wants something different - I've not given in to the demands and thought it would just end. She can spend up to 4 hrs at this wakening the whole house up at screeching point if one of us doesn't go in and place her back to bed. Only to b repeated 10 mins later. Were lost and desperate. We've tried medication, gp checked her out, tried rewards, crying it out etc.... Don't know where to go next