Adderall and prescribed medication

Hey,
My name is Krysten im 14 and im in the 8th grade. I'v been taking adderal for almost 4 months now. Before taking adderal I wasent doing good in school, I would always get into fights. My life was miserable. So I asked my doctor if I could try adderal agian. Before when I took adderall my stomach hurt and I wasent feeling the same. Then I wanted to give it a try. A week after I started to feel my self agian, my family and my teachers noticed a huge diffrence in my academics and my ADD. I went from getting E's and D's to getting on the honor role last quarter. I got the most improved in my grade and I was very happy. Now its the final quarter and now im feeling that adderal isant helping as much as it use to I'm worring about if I'm going to do as well as last quorter and im feeling a little anxiety. I went from taking 30 - 40mg in less than a month, Since I take 10mg after school. I also have been exeirencing weird things. When I get up from sitting down, I sometimes get a huge headach, I cant breath for about 30 seconds, I sometimes see stars and Its like a black out also, I get up then I cant see anything its all black, then slowy I can see agian. I would really like to know if i should raise my Mg higher for me to focus more and be happyer over time. I think adderal was a life changer for me. Please answer my question as soon as poosible!