oil pressure sensor

Make sure you used the correct oil and filter, and that the oil level is OK. If all is good, then you likely have bad engine oil pan seals. There are a couple O-rings in the oil pan that seal the oil pump pick-up tube and oil pressure galleys, these O-rings will distort and cause low oil pressure, just like you are describing. The oil pan would need to be removed and resealed to fix this. This takes about 6 hours of labor and parts are inexpensive, less than $100 for seals, sub frame bolts and you'll need to change the oil again.

Change the oil pressure sender, next to the oil filter