1996 Chevy Monte Carlo 96 Monte O2 sensor bad?

Hello there, my 96 Monte Carlo shakes slightly when running, and shakes worse when I start to accelerate, but instantly goes away when I have taken off. And my fuel consumption has gone very bad. I was thining my o2 sensor was making my motor run too much fuel and not enough air. Also when idling, the exhaust is choppy. Am I running rich? The motor's idle itself is still normal though.