How come adderall is so inconsistent?

[Gman24]

I've been taking barr adderall 15 mg ir twice a day for three months. Some days, it has worked great. It actually makes me love doing schoolwork, and even though I still can't focus in class me being able to study at home makes up for it. However some days it causes me to be completely unmotivated. And on the days it doesn't work I'm less likely to get anything done than the times I don't take it at all, because I'm in a bad mood and I am not interested in anything, not even in shows and songs that I usually like (You know something is wrong when The Beatles sound like crap all of a sudden). I've tried everything to make it more consistent like eating a non acidic diet, getting at least 7 and a half hours of sleep, taking it on the same time everyday, and the effects still vary. It's just so frustrating, and I don't want to get a new prescription because it's excellent when it actually works and I don't want to switch to something that ends up not working at all.