It might very well be a combination of all the things you mentioned! This makes it so hard!
My oldest (13) started failing school when I knew she was too smart to be doing so, talked to her (2nd grade)teachers and they toughened up her work, and now as a 7th grader, has been on the honor roll all this year, with good grades in the last few years also.
Now my 2nd child (10).... wow... we're still not sure what to do with her. It was suggested to me several years ago they thought she had ADHD, she was making awful grades, but I knew she was smart. She's really far behind in school and has just recently decided to start catching up. We did IQ tests and the works to find out what was going on. I have not yet taken her to the doctor for ADHD testing for 2 reasons, i was told she'd grow out of it it's her age, and i don't believe in medicating kids for no reason other than a lack of an explanation of what's going on with them. She makes bad choices even tho she knows there's consequences, never stops talking, talks back, sassy attitude when it's not her way, can't leave her little sister (3) alone when asked repetitively, loud, can't sit still, over dramatizes things, i could go on. BUT she's got the biggest, kindest heart of any child I've ever met! She's the first to hug and comfort, or attach herself to our friends (but she get to the point of overdoing it when it comes to some of these things).
After a lot of my own research, and new teachers this year, and one VERY long spring break, i have decided to have her evaluated by a doctor for ADHD. As a 4th grader just now getting into a 3rd grade level, 5th grade is when they start hammering down in school and she will no longer be able to play catch up, but rather fall farther and farther behind. This has been a really tough choice for me, but i feel now after 10 years, she deserves a chance to be the best she can be in her studies, AND with her friendships (this doesn't always go well either although she makes friends easily). There are new meds out there now, ones that only have to be given once a day and don't have the side effects that ridilin has, so there are more options now.
I too have depression that I have battled most of my life (I'm 33), but I stay positive for my kiddos, they mean the world to me! I've been med-free for 10 years now minus a few months of anti-anxiety meds before my hubby deployed (he made it back safe). Just keep your head up, and just do what you feel is right for YOUR child. It took me several years, but i think this is now the best thing for her. We'll just see what the doctor says...
Best of luck!
K.
P.S. she has bad sleep habits, some nights will stay up all night, then we have really bad days those days, then other days will pass out before bed time on the couch watching tv with us. But I don't think anything has to do with you being a bad parent, the fact that you're trying to find out what is best and doing research proves that you are by far a good parent! Good luck again!