Please check for:
- A loose connection on the socket leading to the ignition coil. A loose connection will hasten the life of any electrical component.
- The condition of the spark plug on that particular cylinder. If it's wet with oil then you may need to find out why that's happening. The oil will create an electrical short on the plug and more likely than not kill the ignition coil quickly as well.
If you've been going to the same place for the same problem repeatedly I would suggest that you give them ample time to diagnose the problem in order for them to address and fix it properly or perhaps it is time to find another shop to maintain your car for you.
Give as much info regarding the history of the car to the mechanic as well, as every bit of information you give the helps them that much more in doing their best to keep your car in tip top shape.