i have exactly the same problem as you. my little one will put himself to sleep at night no problems but as soon as he wakes in the middle of the night(which is every night) he wont go back to sleep unless i'm in his bed with him. i've tried sitting on the bed, next to the bed letting him cry but nothing works.
when he wakes he usually calls out "here mummy" over and over in a REALLY loud voice. i've tried letting him call out and one night he went onand off for an hour and then he finally made his way into my room. and more often than not i fall asleep before he does.
hope we both find a way out of this, i'm just glad i'm not the only one