Please help me 😭😭

Every time I eat anything I feel like I gain like 20 pounds 🙈. I know that's not the case but I just regret eating anything (I don't eat a lot). I have prom coming up so I've had my focus completely on my physique. I feel so miserable rn. I hate feeling like this but I don't know what to do. I can't gain any weight rn. I keep eating less and less but even if I eat one thing I feel terrible.