You should hook up a mechanical gauge to see if the one in your dash is reading right. If it is you have a serious problem, loosing oil pressure is a good way to seize your engine. Check the trouble code for your check engine light and see what that is. I don't know if your car will throw a code for loss of oil pressure, it usually has its own light. If you really are loosing oil pressure get it fixed or you will be walking soon.