How dramitical I change from yesterday to today.

I've noticed lately that I have many good days and a lot of bad days. Yesterday was a terrific day and now today after lunch it became horrendous. For lunch I had a cheeseburger for the first time in almost 5 years. And now I am regretting every little bit of it... I came back to the dorm and took a nap, hoping it would make me feel better, it didn't. I was hoping to god that it would. I woke up feeling worse about my self. Hannah wanted to play tennis, so instead of isolating I went out and played tennis. My confidence went down even lower. I wasn't hitting well at all. I couldn't serve. I was just a hot mess. Then dinner came a long and I really liked what I had, the whole time I couldn't stop thinking about, maybe you should start cutting back on food. You're eating a lot and not working out or playing enough tennis, you're going to get freshman 15 if you don't change your eating habits. My mind just kept on going, So about 10 mins ago, I went onto 100 why to recover. And I read about maybe 20. And my mood is still down. I have been fighting tears for like the past hour. Because my best friend isn't sympathetic. She would just be like "Oh" And then go back to what's she's doing. I don't have anyone here to help me, if you read this please inbox me advise.