If you are/were getting 20 psi of oil pressure, then you were doing fine. The factory manual calls for 20.
Take the filter off and just turn it over,don't start it. There could be enough sludge to clog some or all of the oil passages.If it is good, it should gush oil out where the filter screws on just turning with the starter.
After the above, I would pull the oil pan and see what is going on in there. It is the proverbial "10 minute job"
to get it off, but you will probably need a new oil pan gasket. It will give you a chance to clean out the oil pan, and check the main bearings and rod bearings. I seriously doubt that the oil pump failed, but anything is possible. If the pump is bad, changing it is not a tough job.You'll have to drop the pan. Just unbolt the pump and pull it. Let us know how it turns out.