College Student Needing Help

Hello All,
My name is Trey. I am an 18 year old 5ft 8in 250 lb asthamtic male. And I want to and need to get my weight and my health in check before I do serious damage.
It has come to my attention that I am not only overweight, but becoming increasingly unhealthy. I am a college student who, at one time, weighed 250 lbs. I lost a lot of that weight over the course of my junior and senior year of highschool until I was down to 180 lbs. I did this through diet and exercise,but also from the side effects of my ADHD medicine I was taking, Vyvanse. I felt great and was the skinniest I had been. The feeling did not last long, however. I stopped taking my Vyvanse and gained a slight amount of weight due to the fact that I could no longer work out as hard in my fitness class becuase it was golf season and the coach did not want me to strain myself. After graduation I continued to become more and more sedintary and gained more and more weight, but was still at a healthy level. I got to college and had to start taking my Vyvanse again becuase my ADHD and being in college. While there I started eating even more unhelthy and eventually put on the University of Missouri's version of the "freshman fifteen", the "Mizzou Twenty-Two", even though I was taking my Vyvanse. I am currently finished with my first semester of college and weighing 250lbs once again.
Overall I need help. I am still taking my Vyvanse becuase I am currently working and it helps me concentrate. I don't no where to start or what to do. I know I need to eat healthier and get active, but I don't know what to eat or how to be active without sending myself into an asthma attack. I will be going back to school and I really dont know how that will effect me going through another semester of it again. PLEASE HELP ME!!!