Is being workaholic a sign of depression?

It's not a sign on it's own.
First off don't be a bitch and look for accepted reasons to be depressed. It's easy and dangerous to talk yourself into a depression. Now if you're really depressed ask for help.
Go to a expert or read books of experts or self help.

For example the subtle art of not giving a fuck
https://amazon.com/gp/aw/...

Ryan holiday the obstacle is the way(personal favorite)
https://amazon.com/Obstacle-Way-Tim...

No it's not, nor is it necessarily a bad thing it really depends on your individual needs as a person.

I've read alcoholic... I could relate... But nah