What is wrong with my oldsmobile 88?

It is a 1996 oldsmobile 88, it started running and sounding rough about a month ago and has steadily been getting worse. The whole car shakes when pressing on the gas and when just sitting at a light idling, I think it may have something to do with a sensor somewhere, but I don't know which one and how to fix it. Today I was leaving work, and I had the gas pedal floored pulling onto the road but it took me about 30 seconds just to get up to 20mph, and then it shifted really hard into second. It did that for a while, every time I stopped it would take a long time to get up to the speed limit, then all of a sudden it started getting gas again and I was able to drive normally other than the rough sound of the engine and the car shaking. I am stumped and need help. I have to fix it because I can't afford a new car and I have to get to work.