Q: Oil light comes on for a few seconds only when idle

Approachint a light i stopped on a hill last night. My oil pressure light came on and went right off. It did it every time i idled so i put oil in it after checking (it was low) and the light still sometimes comes on at idle. The car runs fine and shifts fine and its only when im stopped and in drive. As soon as i let off the break the light goes off. I imagine if it was the pump or somethint serious the light would stay on no matter what. Could it be the sender? Or maybe it needs an oil change? Maybe a pump after all? What does this sound like ? Any help would be appreciated as i only have the money to get one thing fixed so I cant afford to play the "fix the cheapest part and then keep going till you figure out the problem" game. Lastly is it safe to drive? I havent driven since the light came back on but its my only way to work tonight and the rest of the week.

My car has 118000 miles.
My car has an automatic transmission.