95 Ford mutang V6 oil pressure

Hello 2carpros. Com my mustang for the past 3 months ive been noticing wen I drive the car for 30 mins. At every stop light the oil pressure gauge starts to move up and down (tweaks) n starts to lose pressure little by little until I accelerate goes up to normal and then again wen I stop. Its also in normal wen its in park. So I turn it off let it cool down for 2 hours and its back to normal then 15 mins. Later happens again. Althought wen the oil pressure is moving up and down(tweakin) my car doesnt even shake or vibrates. Ive onli had the car for 4 months now as soon as I got it I did oil change n recently changed it again.I appreciate for help thank you