I have been taking Adderall XR, but its starting to wear off, is it supposed to?

I am a 17 year old girl. I have been taking Adderall XR for almost a year now, and it has been working great. My grades for the first time are all A's and B's,and my emotions are under control. Before Adderall my grades sucked, C's and D's even F's. Naturally I am an emotional person, but under the medication my emotions weren't that bad. The side affects for me were loss of appitite, sleeplessness, and my personality totally changed. I am a very happy, perky, loves-to-laugh kind of girl. Seriously, one of my favorite hobbies is to laugh. But since the meds. I have totally changed. I am more quiet, lathargic almost. A few weeks ago, I noticed a change that after taking it, it had no affect on me. At first I thought that, that maybe it was just one of those days, but it wasn't. I started feeling like how I used to, tered, not focusing on school, more crazy, loud, sarcastic, mean even. I'm pretty sure that I have built up a sort of immunity to it, am I supposed to?