My tires in car keep going flat

Just bought a 2014 ford focus in December. Love it. Last week, i got a flat in the front passenger one. Got a new tire, drove great for a few days. Today, the light went on indicating that the pressure was low, but in a different tire. Stopped at a gas station, had them fill them up, light went off, drove home fine. Now i go outside a few hours later to run to the store and the tire is flat!

Added (1). There's no holes in the tire once my mechanic looks at it.

Maybe you ran over a bunch of screws or nails that fell off of a truck. This is common when multiple tires are going flat.

No idea? Box of screws dropped on your street is one possible reason. Happened to us years ago when a neighbour had a box of fence staples tip over on the back of his truck. Everyone on the road got at least one flat that week.

You go to the tire shop, get them to fix the flat and they will be able to tell you the reason, show you the screw, or nail, or faulty valve, or whatever.

If you keep driving over nails and screws just what do you expect? Sounds like you needed 4 tires not just One.

You're talking about two different tires. A new one and the one that went flat. Obviously there's a leak or the valve stem is bad.

Doesn't have to be a hole in the tire for there to be a leak. Obviously there's a leak. Find it and fix it and if your mechanic isn't up to it find one that is.

Are you sure the gas station put in Winter air? You do know that it needs to changed in the Spring.