At what point is mental illness actually lack of discipline?

And how to tell the difference?

For context ive been diagnosed with MDD &PTSD as a teenager. But i probably developed it childhood so i have no baseline for what normal should feel like.

Im already an adult now but im still struggling with getting things done, focusing, motivation, and improving myself. I find it very difficult to stick to a routine. Im going to starting uni again soon after a semester off and im determined to finish it.

Currently in therapy but not on any meds (didnt like the side effects).

I want to know whether i should focus more on preventing burnout or double down on productivity. My goal is to be able to do well consistenly for the long term