A couple things come to mind.
First would be as stated by Joybill. If you purchased a cheap replacement like Stant or some other off brand, these don't last more then a year from other people's posts here on the forum. Get an ACDelco from the dealership.
Second, is the reservoir full? Have you added any coolant to it lately? If so, are there visible leaks anywhere? If nothing is on the ground, look under the waterpump and see if there is any orange jelly-like substance under it...if so, you need a WP.
Third, headgasket...which is not an easy task or cheap....
Solo Street Race exhaust
ASAP T2 stripes and badging
Windrestrictor V2 lighted in white
Windrestrictor lighted door sills lighted in white
DDM Works IC Piping
Undercar LEDs in white to match Windrestrictor
ZZPerformance dyno tuned - 286HP, 317ft/lbs of torque at 23psi of boost.