My daughter (19) has had alot of problems with eczema, too. She would scratch her legs in her sleep, which only worsened the condition. We tried and spent so much money on so many lotions and treatments, which never really seemed to help. I second hipchickie's suggestions to try and find the triggers. Eventually, we learned to use simple, free-of-everything soaps for the shower (Ivory) and the one lotion that seemed to help the most was Gold Bond Ultimate with Chamomile. Anna has finally learned how to keep her skin moisturized regularly, which I think has helped. (Either that or its getting better as she's getting older.) As the weather began getting colder, she really started lathering on the moisture, and so far, she's kept it all under control.
Good Luck. I know how it feels to have your child suffer with this.