Body Image Issues [could trigger some people, idk]

I'm 18 years old, 5"6 and 128 pounds (which fluctuates all the time). I've always been really active. I play basketball and work out 3-4x a week. At the beginning of my high school career, I weighed 140 lbs and was severely out of shape. I didn't even realize it until I started playing soccer and was just always tired out much faster than anyone else. I dropped a lot of weight through eating healthier and joining the local gym. I have felt pretty great all up until this summer... I am CONSTANTLY thinking about calories, exercise, weight, working out. I try to eat healthy all the time, but fail time and time again because bad food tastes so freaking good. I feel myself gaining weight back, but I don't know if it's in my head. I'm also constantly bombarded with seeing Instagram models and the desire to look exactly like them. It's all just suffocating me and taking the enjoyment out of my life. I just don't know what to do and how to fix this body image issue. How do I gain the motivation to lose more weight? Or how do I try to just be happy with myself? Has anyone else ever felt like this? [No hate please. Sorry for ranting]