I'm a size 0 but i still look fat

Post a link to a pic and we will give an opinion. It sounds like body dysmorphia.

The size you are is tiny. You need to find some counseling to realize that no matter what you are a child of God and God don't make junk. Learn to Love yourself as you are. The size of your body is tiny, if you feel like your "yummy sticks out". Stand up straight get a straightening or something and hold it up to you stomach and you can actually see that you tummy don't stick out that far.
I admit tho, I understand not liking yourself for various reason. When I was 13 yrs old I came to realize I am a male crossdresser. At 13-14-15 yes of age, I had no internet, no social media to interact, or ask for opinions. I felt like I was The only guy in the world that had a like for wearing bras, or other lingerie. So many times I considered suicide. But in the end I learned I can like myself still. Don't be afraid to talk to someone that can help.you feel good about yourself again.

That's a psychological issue. You need to speak to someone about body image.

It sounds to me like you look fine, but you think you don't.

Yeah your body image is fucked. You think your fat when you clearly are not.

You're fat

It’s possible to have a different body shape from those who weigh more than you, or if you lose weight too fast you can maintain a bit of a belly. I think it’s just your body shape and that you should embrace yourself and find clothes that accentuate the parts of your body you want to show off. I’ve had a hard time accepting my body but I’ve found carefully choosing the right clothes can make all the difference. It seems to me your body weight is right where it should be, so I think you’re healthy but just need a healthier mindset to accept who you are.

Body dismorphia it was called i think
When u see a completely different image of your physical form than it actually is

you are obviously anorexic. a size 0 could not be fat, no way, impossible, I would recommend weight lifting to tone your muscles but I don't think that's your problem. You need treatment for anorexia.

Your BMI is normal so it's probably psychological. I wouldn't put too much stock into dress sizes though. I'm a guy so I don't know for sure, but I'm fairly certain those sizes are pretty subjective so a size 0 at one store maybe a bigger size at another store.

You say you run and eat healthy so chances are there is nothing objectively wrong with your body size, but if you are still worried go see a doctor and make sure your within a healthy weight range for your height. If the doctor says your fine and you are still worried then seek counseling to possibly learn to be more accepting of your image.