Q: Shifting issues, check engine light on

I was driving the car the other day and stopped it for a while. After I started it up again, the dash showed the check engine light on. I put it in reverse with no issues. However, when I put it in drive, there were some problems. The engine was revving. I had to shift into first gear and then to drive in order to get the car running. I put a quart of transmission fluid right away. That helped a lot and it shifted and ran fine. The check engine light was still on though. However, the next time I was about to drive the car, it had the same shifting issues. I couldn't go into drive directly. There were also lights indicating that I am in both drive and park simultaneously. How is that possible? What do you think is the issue with my car? I appreciate your help.