Hi Polly!
Are you currently hosting a Daily Stand Up? I'd think that this would be the fastest way to find out if new User Stories have been assigned to you.
As far as notifications, have you turned on Notifications in your settings? -> Click on your AVATAR -> MY SETTINGS -> NOTIFICATIONS RULES. Under Work Product Type, select USER STORY. Select the box for "Notify me about changes to My User Stories (and items directly related to them). You can also get the My Notifications app on your dashboard once you set it up. I am wondering if this applies to only existing User Stories though or if it'll work for NEW ones as well.. I'd have to test that theory.
Also, you have to turn on your E-mail Notification settings in your Profile. Your sub admin would have to turn this on if it is not turned on already.
If that does not work, I'd ask your teammates, or whoever assigns work, to add you *** a "Watcher" to a given User Stories (it's SUPER quick and easy!), that way, you'd receive the notification right away when a new US is created, but once again, your E-mail notifications must be turned on.
Have a great day!
Kalina