I highly suggest "Savage Continent," (2012) by Keith Lowe, which deals with the immediate post war years specifically and shows how they were integral to the formation of modern Europe. Lowe goes over your exact question in detail and I think you would enjoy the read, he maintains a nice balance between a very readable, almost novel-like approach and a scholarly approach to his writing which makes it easy to digest. While detailing with the situation of ethnic Germans, Lowe also goes over the plights of most internally displaced people's in Europe immediately after the war, but if your interest is only on the Germans, you can still find your answers there