Theres your problem. Your doing more damage to your car by starting it up and not driving it.
The car has to be driven to keep the engine from getting full of soot.
When you set fire to something you get water, this water sits in the exhaust and when the engine gets hot it's slowly burning it off.
Stop turning the car on for the time being, change the oil and when you pass your test take it for a good run down the motorway!