I would get it checked out to be sure.
Temperature will change tire pressure.
If it has been getting cooler outside it may change your tire pressure.
It will be affected more if there is moisture in the tires. Some fill stations fill your tires with moisture. If you notice the nozzle getting wet, your problem getting a lot of water in the tires.
Not that that would cause it to leak, just fluctuate more. If it is constantly going down you may have a slow leak in tire or valvestem. Tires will seep air over time, but it takes longer to do so than a week.
Also I'm sure you just have regular caps, but some caps let air out to a certain PSI. I think those are mostley used for racing though.
1998 Camaro A4 7.06 @ 96.5 MPH NA 1.47 best 60ft
1996 Camaro Convertable (work in progress)