What is wrong with a 2002 Pontiac Grand Am when "Service Engine Soon" & "Trac Off" signals are on?

Car worked great as usual Sunday night when I parked it, but on Monday a.m. it acts like a gremlin took up residence under the hood. Reeks of gas; racing engine; slow shifting; & a tank of gas usually lasting 2 weeks is now down to about 5 days. ETS? Wheels speed sensor not working? No $ for mechanic, so I hope there's an easy answer here! THANKS!!!