Rashi: You pressed and saddened me, to the point that this was a witness of my sin, to prosecute against me.

Ibn Ezra #1: This is an expression of tying, like Chachamim said.

Ibn Ezra #2: This is like "Kumetu v'Lo Es" (22:16; they were cut off before their time.

Malbim: He personifies his pain, as if it caused all these evils, and now it is a witness against me. Since my body and children were punished, and I scream about injustice, they prove from this that I am a Rasha. In the old days, when they wanted to test a person suspected of theft, murder and other Aveiros, they gave to him harsh afflictions, and looked at his face. If it seems that he does not feel them, they acquitted him. If he screamed, this shows that he is guilty, and they afflicted him more. Iyov said, so you say that my screams show that I am guilty!