How to talk about mental health concerns without being dismissed?

Sounds like you've experienced some medical gaslighting, I'm sorry you had to go through that, it can be very disheartening. Not being taken seriously is unfortunately part of the healthcare system and you need to really advocate for yourself. If your doctors brush you off, tell them that you would like to be evaluated/treated anyways and if they refuse ask them to write that in your record, that they refused to treat you. Force them to confront their own biases. I would also like to mention that no illness or disorder is lesser just because you may experience it at a lower level than other people do. I don't have panic attacks anymore and even when I did they weren't very frequent but that doesn't mean I don't have anxiety. All these things are different for everyone and if you think you're experiencing disordered eating then you probably are. Recognizing this is an important first step and I think any good doctor will be happy that you are taking steps to get help. It can't hurt to bring it up to your therapist and explain some of the reasons why you believe you may have this disorder. The possibility of treatment is better than no treatment at all. I wish you luck in your treatment seeking journey! You can do this, don't let the bad doctors cause doubt, believe in yourself and your knowledge of your body - you know you best