2004 Chevy Cavalier

My 2004 Chevy Cavalier has been running rough
it's hesitating especially up hills and in Reverse
where it's almost dying out it has a terrible exhaust
gas smell when we get home and we get out of the
car and we smell it.....I've changed spark plugs and
I'm about to change fuel filter today, I don't have
tons of money so I'm trying to narrow some things
down the check engine light was never on when it
started doing it a couple months ago and then the
car  had a hard time starting the check engine light
came on spark plugs done the check engine light
went off and now the check engine light is back on
and but there is no smell of exhaust and Rod gas
anymore anybody can help me?? Also when the car
was doing it I did have the car scaned to see if
anything was showing up with no check engine
light on and nothing,bno codes came up.... :(;
please help me??? Some suggestions