My daughter was in childcare full time for 14 months, and the only time I had trouble with separation was when the regular worker was on leave, so my daughter had to cope with an unfamiliar person.
However, this all changed when I changed her to one day a week instead of 5, spending the rest of the time at home with me (and after a few weeks her new sister). She would cry and scream for me to take her with me when I left. It took about 3 months before she settled down again, and is now reasonably happy when I leave her.
I've found it best to just say a quick goodbye, and go, even though it is hard with her crying for me and calling my name. If I am concerned about how upset she was when leaving, I ring about an hour after I have dropped her off just to reassure myself that she is okay. This is better than going back, as the staff can let you know how she is without her seeing you, and becoming more upset again. I have found that even on her worst days, by the end of an hour she has forgotten all about being upset at my going, and is joining in, and reasonably happy. On her best days she is already settled and playing happily before I leave.
At home I still find my daughter follows me around, and doesn't like me out of her sight, and will even cry and scream if I go out and leave her with her father. It is hard to leave them when they are like this, but I believe that they do start to learn that you will come back, and start being less concerned when you leave.
Good luck and keep perservering, it does get easier.
mum to 2 girls