On the dog
A development of the well-known phrase "hair of the dog", being on the dog originally referred to drinking large amounts, but can also be used to refer to being on the ball with things such as work and sport.
Hows the work going mate?
Yeah really well, I'm really on the dog at the moment.

Hows the training for that 10k race going?
Not so great, I've fallen off the dog a bit, I'll be back on the dog properly next week though.