Jamieson, Fausset and Brown on Jeremiah 20:8

8. Rather, "Whenever I speak, I cry out. Concerning violence and spoil, I (am compelled to) cry out," that is, complain [Maurer]. English Version in the last clause is more graphic, "I cried violence and spoil" (Jr 6:7)! I could not speak in a calm tone; their desperate wickedness compelled me to "cry out."

because--rather, "therefore," the apodosis of the previous sentence; because in discharging my prophetic functions, I not merely spake, but cried; and cried, violence ... ; therefore the word of the Lord was made a reproach to me (Jr 20:7).