How to help my sick little lamb. pot bellied and freezing, very weak!?

On a recent trip out our grazing hill we came across a very poor little lamb, she is extremly pot bellied and weak. We took her in and she spent the night under a heat lamb with our other pet lambs, she was very eager to drink though we only allowed her small amounts of milk, she will be around about 6 weeks old. but this morning she refused to eat and now she has gone extremly cold in the mouth and is doing he death head throw as we call it. we have taken her in and she is sitting wrapped up in blankets near the heater and slowly warming up, what else can i do to help her? i should say we have no easy acsess to vets.