Unhealthy relationship with food

I’m an 18 year old college student, and ever since last semester my appetite has been decreasing dramatically. It wasn’t intentional, but now, (as much as I hate to admit it) it is. Some days I’ll only eat one thing, like a protein shake or a small sandwich. If I eat more than that, I feel guilty and fear that I’ll gain weight. I’m currently at about 146 pounds and I hate how my body looks. I know it’s the wrong way to go about losing weight, but it’s working and so I keep on doing it. I just want to know if anyone has experienced anything similar and if anyone can offer me advice.