2004 Chevy Trailblazer Oil Gauge Moving & Check Engine

This was happening for about a week or a couple of days before the check engine light came on. When the car is in idle, the oil gauge goes down to the middle. When I accelerate, the gauge goes up to the notch past the half mark. Also, the check engine light came on while driving the car. I checked the oil, and it's full. I have my suspicions that the check engine light is on because of the oil gauge going up and down.