Greenhouse gas also reflects infrared energy coming from the sun?
If greenhouse gases trap infrared energy, why is it not also reflecting the same infrared energy coming from the sun away?
It does. However most thermal energy from the sun is at much shorter wavelengths and passes through the atmosphere unhindered. It warms the earth's surface (think of stone or sand on a sunny day, it can get too hot to touch). These warm surfaces radiate long wavelength infra-red and greenhouse gases trap those. That's the whole point. See
http://en.wikipedia.org/wiki/Greenhouse_effect for the details.