Got diagnosed with severe depression. How to climb out of an abyss that actively stunts my will to work?

I've been on meds in the past (4 out of the last 6 years) but my psychiatrist never told me my exact diagnosis besides anxiety and depression. I started therapy recently and my psychologist took a depression inventory and told me I've severe depression after evaluating the score. I can afford therapy only once a week and it's a very slow process because we can't really cover much in 45 minutes.

There's a lot of work to be done from my side professionally and I just haven't been able to achieve anything in the past few months. Getting out of this inaction and achieving a basic level of productivity, health, and hobbies are crucial for me.

I've seen Dr. David Burns's Feeling Great being praised a lot for its accessible approach. Does anyone else have any experience with the book?

Also, what can I do to get out of this hole? I want to get better but don't have any will to move. I don't know how to tackle this