Rashi: He returns to his initial complaint (You raised me and cast me down, my days are like a shadow - verses 11-12). You afflicted my strength via my enemies.

Radak: Each of the Bnei Galus desires to see the salvation, and fears lest he die soon and not see it. The enemy afflicted my strength on the road. Due to the affliction of Galus and harsh masters, a man toils to travel in Galus from place to place - perhaps dwelling elsewhere will be better. The toil weakens and shortens life.

Malbim: My strength was weakened via the many exiles and [forced] relocation.