I have already been prescribed Adderall

But after my last discussion with my Psychiatrist, it seems as though it's pretty much up to me to determine if I "need" it.
When I'm on Adderall (20mg or 25mg, I have both now), I definitely feel more motivated. Though I understand anyone probably would. I feel more capable. I don't believe this is a placebo effect, but who knows? I know there have been times when I've been on it where I haven't wanted to do whatever is in front of me (e.g. work), when I have had a desire to specifically not do it.
Maybe I just don't get enough sleep. Maybe this is a self-esteem issue. I just don't know. I go off Adderall for months, and then take it for a while, and then go off of it again. Maybe I'm expecting it to do something it's not supposed to do. Maybe I'm just not motivating myself enough. I just dunno what it is. Can anyone offer insight?