What book are you using? I'm using the violin version of this book, which is a real helpful book, so I imagine the viola counterpart would be, too. *link for Introducing the Positions for Viola*
World's Okayest Fiddler
I also just began with 3rd position a few weeks ago. First assignment from my teacher was to go learn the names of the notes in 3rd position on each string.
Oh man, was I shocked to find myself coming up blank on something I thought would be a breeze.
So I had to revert to a position of (uncharacteristic) patience. Instead of learning all of 3rd position in one week, I went and did one string a week. Now I'm getting to the E-string and it's just starting to sink in.
This is the book I'm using: