"Check Oil" light intermittently coming on

Hi, I have a 1995 Pontiac Grand Am GT with a brand new 3.1L V6. I just had a oil leak last week. When I took it to my mechanic he said it was a blown oil sensor leaving the oil pump pushing out oil whenever the car was running, and the unneeded oil was leaking out. He replaced the sensor and the car was running great again, however today the "Check Oil" light came on again whenever I was idling. I checked the oil and its just a tad over full, so I dunno if that would cause it. It's also just passed the 3 months for the oil change, but I haven't put that much mileage on it so I don't think its a clogged oil filter either. Also, my oil pressure gauge is not reading at all, its stuck all the way to the left and does not move so I think it could be the new oil sensor he put in is faulty. Any idea on what the cause is?

I would think it the sensor or the harness may have come loose or off.