Oil pressure on Pontiac Firebird

I have a 2001 pontiac firebird with 132,000 miles(I travel quite a lot) and I have been having problems with my oil pressure. My oil pressure constantly drops and then will pick back up and drop again. When I was working on my car I ended up having to change my relay and water pump and flushing my heater out. My car worked fine for about 2 weeks. Now I have no oil pressure and my check gages light is on. I am sure that my oil pump has given up the ghost. I called different auto parts stores and the places I spoke to had no information on that part or could not get it for me. I called another place and was told that the oil pump is built in the block and I would have to buy a repair kit. I just want to find out if this is correct before I buy it.