“I don’t drive the car very often so I haven’t been changing oil by the maintenance schedule”
Based on what we have been told (with significant gaps in information), it sounds like this engine is probably filled with oil sludge. For the benefit of the OP’s wallet, he/she should read the maintenance schedule for the next car much more carefully, as almost all of the scheduled maintenance has both an odometer mileage factor and an elapsed time factor, with an “either/or” proviso and a “whichever comes first” proviso.
The elapsed time factor is to prevent problems like oil sludge in cars that accumulate miles very slowly. Unfortunately, it seems that many people can’t seem to comprehend those provisos in the maintenance schedule, and premature death of the engine is the frequent result.
So, with the available information, all I can say is that it is very possible that the only short-term solution at this point is to replace the oil pump…even though the engine may have already sustained damage from running with a low oil level, from going too long between oil changes, and (possibly) from using the wrong type of oil.
Replacing the oil pump should make the car drivable, but then the question remains…
How much longer will it be drivable with the original, damaged engine?