I am 13 and worried about my weight. I want to be a model, but I store lots of fat in my face, thighs and stomach. Is that genetic, or is it from me not eating right or exercising, and because I’m not done growing? I come from a tall family, so I probably will end up taller.

I look at myself in the mirror, and then go in my room and cry. I point out all my flaws, even things I might not have. I’m scared to talk about it. My parents think I’m insecure when I say how “ugly” I am, and reassure me I’m gorgeous. My friends are shocked when they find out what I weigh, because they never see me as fat. I wear baggy clothes and try to hide myself. I do facial exercises to try to slim down my face – to be pretty. I cry in my room for hours until I can’t make any more tears.

I don’t know what to do. I need to exercise, but I don’t have a good exercise plan or know how to stay motivated. I want to diet, but teenagers aren’t meant to. I’ve self-diagnosed with BDD (body dysmorphic disorder), too.

I don’t know who to talk to. I hate myself. I am my own enemy and I hate it.

Your letter was heartbreaking. So much angst at 13. That was me, too, hating my body and spending so much time railing against what it wasn’t, instead of looking at what it was. So I understand a little of how you feel.

I showed your letter to consultant psychiatrist Louise Theodosiou (rcpsych.ac.uk), who specialises in working with adolescents. The first thing she (and I) wanted you to know, is that you are a young person “who is thoughtful and a detailed thinker”. Theodosiou works predominantly with 16- and 17-year-olds at the moment, and “it’s not often they have the level of detail you do”. But I think this thoughtful nature is working against you, rather than for you.

“I was concerned by your letter,” said Theodosiou. “One of the things we don’t want for young people is for them to be distressed. Often the first place people go to is family members, but you seem to have trouble accessing that.” Your family may not understand the level of your distress and because of that, their reassurances may not ring true to you (even though I’m sure they are). Or they simply may not know how to help. Is there anyone else you can talk to? A school counsellor? Or your GP? Because you need to talk to someone, and your GP should be able to refer you to people who can help. I know you are scared, but talking to someone who is trained will be of real benefit. It’s much better than talking to a friend.

I was 21 before I got help, and it changed my life. I wish I’d gone earlier. I wish someone had told me that as you enter puberty and your body changes, so does your brain: that it goes through the most intense period of rewiring since you were a toddler. That at no other time in your life will you feel so self-conscious, and things that really, really bother you now just won’t assume such epic proportions as you get older. I wish someone had taught me about nutrition and all the beautiful and amazing things a strong, healthy body can do instead of me focusing on Photoshopped pictures of models in magazines and finding myself lacking.

I have not printed the details you sent me, but you are not fat; and you are very probably not “done growing”, so you shouldn’t diet at this age. Staying fit and active – within reason, don’t overexercise – will help your mind and body stay strong. I worked with models for a decade and very few of them were happy with themselves. Being what you may think of as thin or pretty doesn’t change how you feel inside.

The way you feel about yourself appears to be wrapped up in your physical appearance, but this self-hatred is a symptom of something else – and it’s this that needs to be worked out and worked on. Then you will see your confidence soar.

Theodosiou was concerned about your self-diagnosis of BDD and wondered where your information was from – I’m sure you realise there is good, useful info out there and also some that isn’t accurate. Proper diagnosis of BDD can only come from a psychiatrist.

I’ve put some links to websites you might find helpful below. Please talk to someone, get help and I promise life won’t always be like this.

• youngminds.org.uk; childline.org.uk; rcpsych.ac.uk; agnesforgirls.com.

Send your problem to annalisa.barbieri@mac.com. Annalisa regrets she cannot enter into personal correspondence