Is it possible that there's just a personality clash? What you've described sounds like my DS - initially it was all good, then all of a sudden he'd start to cry as soon as we got in the front door because he knew I was going to leave him.

Then that FDC lady went on holidays and we filled in with someone else and he was just a different little boy. He even cried when we went home once, he is just so happy there during the day.

Honestly I thought it was a separation thing that I was just going to have to learn to deal with, but as another poster said listen to your gut feeling and if it isn't right keep looking. It may be a personality thing.

Hope things are looking up for you soon