Thank you for the comment!
There is an indicator for the amount of energy you have left, but because I messed up the UI scaling it only shows in fullscreen.
Pushing should work by holding both LMB and RMB, but if it didn't work for you it might be a bug I'll have to look into.
I'll probably rework the bullets once I have clearer level designs so I can plan accordingly.
Edit: I made the game launch in fullscreen mode by default now, in hindsight I should've done that from the start.