A couple of things to check. First is easy. Make sure you have plenty of oil. Low oil can give a low pressure reading. Second, sounds like your oil pressure sender unit is going out. It is located right next to the oil filter and has a wire going to it. You may need to get a manual pressure guage and check the pressure that way. If you decide to replace the old one it is easy to replace and not too expensive at an automotive store. Many people recommend replacing with a factory OEM unit, about 60 bucks or if you go aftermarket, you are looking at about 30.