My engine is running very rough. The Check Engine and Trac Off lights are on.

My car was shaking pretty bad when I started it, then smoothing out as I drove. The coolant level had also been dropping, although no leak was ever found. I started experiencing some loss of power while accelerating and the check engine and trac off lights came on, so I stopped into an autozone to get the code on the check engine light. I'm not sure of the exact code, but it was a misfire in cylinder 4. I was told to replace the spark plugs and wires (which had just been done a few weeks before) and the ignition coil. I replaced the coil and my car ran okay for about 200 miles (still losing coolant, but the shaking and power loss stopped), and now I'm experiencing the same problems as before. My oil light also came on for a couple minutes. I checked the oil and it seems that the level has slightly increased, the oil apperas thinner than usual, and it smells like there is quite a bit of gas mixed in with it. I have no idea where to even begin figuring out what's wrong. Please help?