Before coming out as trans and having my previous diagnosis scrapped, I was diagnosed as Bipolar II ( which basically means you have depressive episodes of varying strengths and manic episodes that are mild enough they don't cause a danger to yourself or others and are not uncontrollable--a very tricky diagnosis since the symptoms are quite muted compared to Bipolar I). I also taught special needs kids, including those with mental illness, so I have a lot of experience with psychiatrists and psychologists (well over ten years of it), and while I never encourage people to simply go against a psych's diagnosis, if you are not comfortable with their process or don't agree with their findings, feel free to get a second opinion. Mental health professionals are not gods, nor can they read minds. Also, not all doctors work well with everyone. Though they don't like to admit it, unless something has very distinct symptoms psychiatry is mostly a guessing game. When I worked with ED (Emotionally Disturbed) kids, their diagnoses would change all the time as they swapped doctors. If you feel like you are trans but this doctor thinks you have a "deeper issue" (whatever that means) then you might consider another opinion unless he is SUPER well versed in transgender issues to the point that he has seen hundreds of trans patients. Many psychiatrists don't even really understand being trans and would much prefer it to be something they can attempt to "cure" with medication and therapy. If you think he might be right, then great! Stick with it and find out. But if you think he just doesn't understand then definitely seek another opinion. I know they sometimes make you feel like they know all and you know nothing, but I have worked with these people both as a patient and as a coworker when I was a special needs teacher, and I promise you that they are far from all knowing. Therapy is supposed to help you, and if it's not helping, find someone else to go to. Otherwise you might find yourself giving up on it, which is so not the point of going to therapy!
Someone mentioned they feel a need to stretch the truth in therapy, and that is why I don't believe in gatekeeping for adults. It is also why I went to a different therapist to get my HRT letter than the one I go to for therapy. You shouldn't HAVE to lie or feel like you have to stretch the truth, because any therapist well versed in transgender issues should know that nothing you say invalidates you being trans. Therapy should be a safe space for you to explore your doubts, confusion, etc without being judged. When therapists ask you probing questions that are tough to answer, you should know for a fact that they are doing it to help you discover more about yourself as a person, not as a "test" to try and invalidate who you are. Therapy is based on trust. Feel free to tell your mental health professional if a question makes you uncomfortable and explain that you feel like you are being tested when asked such a question and that it feels like an invalidation of your identity. It might turn out that the question was completely idle and that your feeling that way is something you need to work on through counseling. On the other hand they might very well have been testing you, and you may want to look into finding a more understanding counselor if you are sure you know who you are and are tired of having people question your status.
I am very pro Mental health professionals, but at the same time I always caution people not to award them a god-like status. Like us they are just people doing the best they can, but diagnosing people's problems is no easy task, and sometimes they prefer to stick to problems they understand rather than delve into things they aren't heavily trained in. In that case, second opinions are the bomb. I can't tell you how many kids I saw diagnosed as ADHD who later turned out to be mildly ID (Intellectually Disabled) and just had social issues that a busy doctor quickly translated to ADHD. But at the same time I have seen an ID AND ED paranoid schizophrenic kid go from almost non-functioning to holding a job at a grocery store and happy with their life with help of the right professional. The hard part is finding that right one!