Head Gasket

This question is for saturntech9. On my 2002 Saturn Vue, when the mechanic changed my plugs, and had to replace the gasket b/c of the way he had to get to them, was that my head gasket? When he told me he had to order a gasket I started to google gaskets, and was reading signs of a blown head gasket. Now I'm real paranoid about my car, b/c I'm so afraid of breaking down, so when I read something that has signs to indicate thats what might be wrong with my car, and I have some of the sings I automatically think that is whats wrong. First, if I had a bad head gasket would it have shown up on the computer when they was scanning it? Also, my coolant light was on before I took it to the garage so I checked the coolant and it was 2in below the fill mark, so I filled it back to the line and the light went off, well now the coolant light is back on, so I checked it again and it was almost all gone. I had read that some signs of bad head gasket is coolant loss. And white smoke out the tail pipe with a sweet smell like antifreeze, I have white smoke, but I noticed that almost all cars do, but I can smell like a sweet smell. I really don't know where to go from here I can't afford to take it to a garage, so what do you think? Is there anything I can do to find out for sure myself?