Passenger rear tire - I've been putting air in every day - just started happening. Checked for nails and other stuff - nothing. Anyone else having problems with tires not seated correctly or valve stems leaking?

 

You can take it into the shop, or you can check it yourself. Get a spray bottle, fill it with water and put a little dish soap in it. Start with the valve stem (after taking the valve cap off ), and soak it. If there's air leaking, it will blow bubbles. If you see bubbles... there's your leak. Repeat around the bead and look for bubbles.

If you still don't find anything, repeat along the tread.

If you can't find a leak at that point, you would have to dismount the wheel/tire, and dunk it in a tub of water to find the leak.