alright...this is what i'm assuming...
you drove your car for some time when it overheated and you possibly did blow your head gaskets...the best way to tell if it's your head gasket would be by pulling the oil dip stick and checking to see if it looks like coffee and milk...another way could be checking the oil cap, but sometimes the cap will build a little bit of that "mayo" stuff and it's really not a good indication of a blown head gasket...
another thing that might have happen as a result could be that you cracked a head...meaning that the heads got too hot and cracked...now this could be a reason why your check engine light comes on...if the cylinder cracked and coolant leaks into the spark plug port, it will cause a misfire and it will eventually trigger the check engine light...that little shake at stops could be the misfire...coolant is soaking the spark plug...
it seems by the way you are explaining the situation that you cracked a head and coolant is leaking into the spark plug....a way to check it is to simply look at the coolant resevoir tank...if you notice that you're low on coolant all the time, then the coolant is leaking from somewhere on the engine...if you need to add coolant or if the bottle is empty, then it's a good sign that theres a leak somewhere...
there are a few possibilties, but the most common with your description is the above 2...now to get a diagnosis, at a dealership will cost you about 120 bucks...this is just to hook up the scanner and retrive the codes in the memory and finding out exactly what component is failing....it could be something related to the overheating, but at the same time it could be something totally different...your best bet is to take it to a dealer and paying for the diagnosis...you could take it to an independent shop, but sometimes they don't have access to recalls or technical service bulletins that might be a quick and cheap fix...if it's a common problem , the dealer will most likely carry the part and be able to have the car for you the same day...but start with the diagnosis and find out exactly what the concern is and then decide if it's something you can do on your own...