Peter,
Happy early birthday! Really and truly. In your struggles, you've given me some extra inspiration to go out and get riding, even with our fresh 8" of snow here in MA.
I checked out your new bicycle on Giant's website, and I'd bet money on your tubes having Schrader valves (automotive-style, rubber coated) rather than Presta (narrower, threaded metal exterior). Especially since the GX model has tubes filled with Slime sealant. Unless they're pre-filled during manufacturing, you have to take out the core of the valve to fill tubes with Slime, and that's something you can usually only do with Schrader valves.
Another little carrot--even if you're not riding, no reason why you can't pop off the front wheel and practice changing the tube a few times. Good practice for warmer weather when you catch a tack, thorn, or ten-penny nail.
Keep going!!
John