1996 Saturn SL2 white smoke, bad smell of gas, check engine

This is gonna be lengthy, sorry but I have to explain. We bought this car knowing it needed a O2 sensor. We started out by getting plugs and wires due to code for misfire cylinder 3, did not fix problem, next sensor said knox sensor, replaced that then O2 sensor, light was off for 2 days and I drove it once again and light came back on and great deal of white smoke out tailpipe and bad smell of gas which also goes into car. Now its saying poor connection to knock sensor, mass air flow sensor and misfire cylinder 3 again. I dont know what else to do, gotta get this light off so I can get it inspected.I am at a major loss here dont know what to do next if anything. Oh and when I am shifting gears, the check engine light often will blink on and off till I am not shifting any longer then it is back on all the time, dont know if that is meaning something or not, thank you