After tuning up my car I have white smoke coming from rear of engine and out of tail pipe.

The car was running fine before the tune up. I tuned the car because when I had the car in for inscection the mechanic said the emmisions where alittle high and it needed a tune up. I replaced the spark plugs and wires, removed and cleaned the fuel injectors with carb cleaner, and replaced the gaskets down to the valve covers. In order to get to the rear spark plugs and injectors I had to take the intake manifold off and while I had everything dissasembled replaced the valve cover gaskets. After I put everything back together now I have white smoke coming from the back of the engine and the tail pipes. There was a slight idleing problem but it seems to be fixed once a tightened a few lines. The other thing I am doing is flushing out the ac system. I did get the oil from the evaporator on the exhuast manifold. I am concered becauase the smoke is coming out of both places. At first I thought it was just the oil from the ac flushing; However I am starting to think it might be a different problem. The smoke does look like it is coming from the exhaust manifold and even lower past the pre cat. I need to determine what the smoke is from. The engine was fine before and now there is smoke. The only things that I can think of would be a leaking valve cover gasket, or the ac flushing causing oil to burn. I am almost positive that I didn't crack a head cylinder while replacing the gaskets and I don't understand why the head gaskets would be blown and leaking coolant. Anyway can you please help me determine the cause of the smoke. I am not sure if I should run the engine in its current condition. Thyank You.