three weeks is nothing...but it can easily become three months, three years or three decades if you mess up. Don't push it, please.
I couldn't agree more. Give it the rest it deserves.
However, I find doing deep squats once a day keeps your legs strong and doesn't have to involve your shoulder.
As a newbie you will be excited about this martial art and as you said, trying to soak up everything about it. Be careful you don't burn out both mentally and physically. I have found those students who approach the art gently (both in attitude and physically) tend to stay the distance. Those who jump in the deep end...drown.
For what its worth