Hoping to start a healthier journey

Hey so I am new to this sort of diet and workout-tracking site. I have always weighed more than average all my life. It was never an issue of health, I guess because I was fairly active through the first half of high school with dancing and martial arts. After that, though, my activity level has decreased. As a college freshman, I irregularly work out (I have weeks where i am active every day, then some where I am not at all), finding excuses such as "no time" or "the gym is too far." On top of that, living in a dorm gives me very limited access to proper food. I was 185 lb. before college started and have gained a net of about 6-10 lbs, since I lose some then gain some occasionally. My younger brother has been very motivated to stay in shape, and it made me realize I need to try harder since I don't want to stay unhealthy. I am aware I need to lose at least 45 lbs, maybe 50 to be in the normal range, and that is my overall goal.