The chapter can be divided into four main parts:
Remembrances of better days (Lamentations 4:1–11)
The sins of prophets and priests (Lamentations 4:12–16)
A vain search for help (Lamentations 4:17–20)
Edom's coming punishment (Lamentations 4:21–22).1
Another very similar suggestion is as follows:
Zion's continuing torment (Lamentations 4:1–10)
Rejection by the Lord (Lamentations 4:11–16)
Helpless is man's aid (Lamentations 4:17–20)
The destiny of Edom and Zion (Lamentations 4:21–22).2
1 How the gold has grown dim, how the pure gold is changed! The holy stones lie scattered at the head of every street.