Knocking and shaking in engine with flashing CEL

Hello, first time poster here. I have a 2010 with 190k miles on it and the car has been absolutely fantastic until last week. Started up the car and loud knocking and shaking came from the engine and resolved itself. Drove to work and on the way the check engine light started flashing and stayed on. Drove to the dealership and they wanted $400 to diagnose, so stopped at the aitopart store and code for cylinder 2 misfire was read. I replaced all 4 spark plugs and coil for cylinder 2. Took it out for a test drive and everything seemed great until I put it in power mode and the check engine light flashed 10x and stopped. No codes. I figured it was a fluke, but yesterday the car was really struggling when trying to drive it and the check engine light flashed 3 times. I’m not sure what the problem is and I’m afraid my engine is toast. Taking it to the dealership cuts into my budget for the next car of the engine is no good. I’m going to try cleaning the EGR and fuel filter to see if that helps any but I thought I’d post here to see if anyone has had this problem and can give me some advice. I really love this car and was hoping to get another year out of her. Thanks for reading.

 

Edit: another detail is the spark plug on cylinder 1 had oil on it when changing it out. I’m not sure what kind of an issue that presents.

 

Coolant and oil levels are great. I’m concerned because of the oil in the spark plug of cylinder 1. Would this be indicative of a blown head gasket without coolant level changes?