I am a 21 yr. old girl and I have been taking Vyvanse for about a year and a half. I have had weight loss as well. I weigh about 102 lbs. and I'm 5'7 so my dr. is concerned about my weight. I also have a low appetite and don't eat all day sometimes. But I have learned to force myself to eat. I like getting Naked fruit drinks (they have them at most grocery stores and health food stores) for those times when you know you'll get sick if you eat, since they have like 5 servings of fruits and vegetables and are easy on your body. You could try them out and see if they work for you. I also recommend taking an Omega 3 fish oil supplement since it helps with concentration. (You can get it at most health food stores, pharmacies and some grocery stores for like $6 for 200 capsules).
I would also check out the book "Healing ADD: The breakthrough program that allows you to see and heal the 6 types of ADD." by Daniel Amen. In the book there's a test thing to see which type/types you have. It also has some pretty good advice for ADD. You can see the types online, but they charge you like $4 to take the test online. Here's the website that tells you what the six types are:
If you have been having aggressive behavior after taking Vyvanse, then you might have Type 4 ADD (see website) because it says that taking a stimulant (like Vyvanse) alone can make the person more irritable/aggressive, which it does for me. It says that it's more effective taken with an anti-seizure medication such as Klonopin, which I also take and it helps me out quite a bit since I am pretty sure I have Type 4.
I hope this information helps. The 6 types thing really helped me understand what medications and supplements to take and how my brain is working and how ADD affects me personally.