I Just had my Oxygen Sensor replaced, and my temperature gauge is still on cold! help!?

Had issues with the engine-always felt like the fuel supply was cutting off (and temp was always cold). A diagnostics test said the oxygen sensor needed replacing, although the temp gauge is still ALWAYS on cold. It basically only warmed up once, after i got the new sensor. The car also still seems like it wants to turn off when i slow down or come to a stop.