I've just started, but I plan to create an annotated bibliography of Song of Songs interpretation here. More later...

The Postillae of Nicholas of Lyra was the first biblical commentary to be printed. His Postillae on the Song of Songs was very widely read; it was reprinted in 34 editions by 1550. The word "postilla" apparently derives from the Latin post illa [verba], "after these words" used in medieval sermons; it refers to comments on biblical texts. Nicholas's Literal Postilla explained the Biblical text word by word.

Nicholas was a Franciscan. He read Hebrew and used Rabbinic sources such as Rashi. He knew that דדיך ddyk in Song 1:2 should be translated "amores" instead of "ubera". In his view, the first six chapters of the Song recount the history of Israel from the Exodus to the return from Babylonian Exile, and the last two chapters recount the history of the Church to Constantine.