1)
Why does it say Za'amcha"?
1.
Radak: If not for Your anger, I would not be handed over to the enemies for so long.
2.
Malbim: I ate ashes in place of bread due to Your anger, which is Your curse. Via this, "my teeth were broken on pebbles; he bent me into ashes" (Eichah 3:16).
2)
Why does it say "Ki Nesasani"?
1.
Rashi: Initially You raised me, and now You cast me from Shamayim to the ground. Had You not raised me initially, my shame would not be so great.
2.
Radak: One who wants to cast something to the ground, he lifts it up and casts it down forcefully - "Hishlich mi'Shamayim Aretz" (Eichah 2:1). The higher one lifts it, the fall is more forceful.
