Engine on 1994 Oldsmobile 98

The problem with my car this is a knocking and I am not sure where it is coming from. Second I recently got an oil change along with the filter and spark plugs replaced with the air filter replaced. Now if I drive my car for a long distance over 10 miles when I come to a stop light the oil pressure light starts to flash or the oil pressure light and other lights come on an the car just stops and from time to time my check in light comes on. I tried to have that checked at Auto Zone but they say my car is to old. I don't know what else to do. I was that I should have had a oil flush because not my oil is dirty again. Help.

Asked by for the 1994 Oldsmobile 98
Your engine oil pump is probably pumping, when the engine oil is thick it takes less pressure to fill the voids of worn bearings. When the engine warms up the oil, the oil becomes thin and you get the knocking because there is not enough oil getting to the bearings. You may also have blocked oil passages in the engine, that is not allowing the oil to return to the pan fast enough to get pumped through the engine as needed. Engine flush may help, but sounds like damage has already been done.