Missfire on my Firebird 3.8 ? Mechanic keeps adding problems?

2months ago I took my car to a repair shop so they could change the Head Gaskets because water and antifreeze had gone inside the motor and my oil was half water. 2wks later and $1,183.60 dollars later I received my vehicle back but it had a noise like a tapping or something(lifter noise). I took it back to them but they said the noise was going to go away once I ran the car a few miles. about 2wks later My car again was having a hard time running(check engine started flashing on and off). I took it to them and they told me it was a EGR Valve. I payed $190.50 to get that fixed. Now 2wks later I take the car again because the same problem started happening again.. This time I take it to Autozone first and they tell me its a Domestic Missfire. I took it to them 2days ago and they told me that i have a 1yr warranty and that they will take out the lifter noise and fix the 2 missfires #2,#5. free. 2hrs later they call me and inform me that there is an Ignition Coil that is causing 2cylinders not to work and thats why my car is not running well. also the Oil Sending Unit is licking a bunch of oil. and for this it will be a total of $243. because the warranty for the Gaskets and opening the motor doesnt cover this. Im wondering if the Coil and the EGR and the Oil sending Unit were caused by them not fixing the car right the first few times?