Q: I cannot upload new photos to Photo Stream from my Mac Air. Anyone else?

You can't.  The My Photo Stream is only one way now, from the mobile device to the Photos library.  If you want a two way sync you'll need to enable the iCloud Photo Library on both devices.

However, before doing that you should make yourself completely familiar with how the iCPL works and what is required.  It will upload your entire library to the iCloud and can take weeks to finish depending on the size of the library. You'll need to purchase additional iCloud space to accommodate the library.

Here are some Apple documents you should become familiar with before enabling the iCloud Photo Library.

iCloud Photo Library FAQ - Apple Support

iCloud storage pricing - Apple Support

iCloud Library Overview