What is "Imchem"?
Rashi, Targum Yonasan: Your Kenesiyah (gathering congregation). Radak - the same applies to "Rivu v'Imchem" (Hoshe'a 2:4).
What will be the shame?
Radak: You rejoiced when you plundered My inheritance. You will be ashamed when others plunder you.
What is "Yoladtechem"?
Radak: Your congregation.
Radak citing Targum Yonasan: Your country.
Malbim: The land that gave birth to you.
Why does it say "Acharis Goyim"?
Rashi: If your beginning was great, your end will be a Midbar (desolate). Radak - they will be killed, and their land will be a desert.
Malbim: The nations that this land gave birth to, i.e. the ones who dwelled in the land, their end will be a desert.