A Spark Plug Wire Popping up on its own!

I have a 1998 Dodge Avenger ES V6, Over 150,000 mileages, Well I was driving my veh where suddenly my car started shaking when stepping on the gas where it felt like it didn't have enough power. So I check under the hood where I notice that the center Spark Plug wire was pop up "Has if someone forgot to plug the wire back after checking it. Which it was me last night when I was looking for any leaking Oil. Before this happen, I had just replace the wire with news ones at auto service shop which cost over $400 about 3-4months ago, due to leaking oil but since the repairs I didn’t have any problem or oil. Well going back to my question I but back the spark plug wire into the correct position then my car started fine " like if nothing happen!" Until I drove for about 40-50 minutes where It started to shake again. So I looked under the hood one more time where the same spark plug wire pop up again. I am not sure want to do?