I have been using this idiom as sth. being in the process.. e.g.
We do what we can do now and keep adding more on the go. 随时随地..
But seems I heard some other meanings of this idiom.
So I googled, yes, it can also mean very busy.
e.g.
- very busy
He has only one hour left to catch his flight, he is really on the go.
- in the process of being produced:
Did you know that she's got a new book on the go (= being written)?