How do I find out the reason my low oil pressure warning light is on? on 1996 Chevrolet Impala SS

Changed oil 3 weeks ago. Replaced the oil pressure sensor.

Have the actual pressure checked with a test gauge.
1 more answer
Does the car have a guage on the cluster or just a light? If there is a guage, what does it say pressure is? Is the Check Engine light on? Check your oil, then put a manual guage on it and see what it reads. If the dash has a guage and it reads normal, and the manual guage reads normal, then you need to test the Oil Pressure Sensor circuit with a manual instrument panel guage tester.