I'm developing tolerance to Vyvanse?

So I have been taking 50 mg Vyvanse for 3 consecutive days now. I'm not prescribed or properly diagnosed with ADHD but I'm taking it for my finals (I'm well aware of the risks so please no lecturing me about it). First day I felt great, hyper, energetic, happy, and very talkative, I could thinking really well and fast, which is basically what amphetamines supposes to do. 2nd day, not as great, but still feelin it. 3rd day I felt it for only about an hr where its at its peak. I'm feel slow and words are hard to retrieve when I write or talk. I barely felt the need to talk to anyone unlike the 1st day where I was compelled to. Is this my development of tolerance to it or is this what happens to people who actually has ADHD who takes it? Cuz my friends who have ADHD always tell me it turns them into mindless zombies.