My 3 year old won't sleep!

I have a nearly three year old who has always been a pretty good sleeper. Recently though she's been up 10 times each night. Crying for nothing. When she gets up she always gets a small cuddle and gets put straight back to bed(or the toilet if needed). But nothing seems to be working now. If she has supper or not, has a nap or not, takes a drink to bed or not, extra covers, less covers, goes to the toilet or doesn't, has stories, watches a DVD, night light, nothing works!! Any idea how I can help her(and me) sleep all night?? Thanks