Rashi: I am light (lowly) in my own eyes. Radak - the verse omits what is described [as being disgraced], just like "Ki Chamudos Atah" (Daniel 9:23; it should say Ish Chamudos), "k'Eder ha'Ketzuvos" (Shir ha'Shirim 4:2; it should say 'k'Eder Rechelim ha'Ketzuvos')

Radak: The flanks are under the loins, above the thighs. They are near the kidneys; weakness and illness affect them.

Radak citing his father: Nikleh is a noun, like "Kaluy ba'Esh" (Vayikra 2:14). It says so due to the great heat of the illness - "va'Asaledah v'Chilah" (Iyov 6:10).

Malbim: This is inner disgrace that fills his thoughts and Ru'ach. Also there is nothing healthy in my external flesh; my flesh and Ru'ach are both stricken.

Radak: People who cry and sigh often repeat their words.