Any number of things could be going on with your car. It is getting to be high mileage, so you can count on needing some repair and maintenance work, soon. That doesn't mean that you're in big trouble, necessarily.
The Check Engine Light coming on means there's definitely a problem. It may be a complete coincidence that it was after an oil change. Depending on how well you have maintained the car, it sounds like it is time to take it in for a thorough diagnosis and inspection, and invest some money in maintenance.