I am going to go out on a limb and disagree with pegasus, to a point.

Sometimes self-diagnosis is the only option a person has due to financial status, family life (especially in an abusive environment, one must be careful), race, gender or trans status, autistic status, and disability. It can be both dangerous for some, and impossible for some, to have an official diagnosis with a professional done. Socioeconomic status also plays a huge role here.

For example, one of my friends knew she was autistic her whole life. Especially when she self educated herself and spoke to others. When she finally left home and her university offered her a screening, alas, she was diagnosed as autistic.

There is nothing wrong with self diagnosis. Especially if getting to a doctor is an impossibility for the individual in need of diagnosis. It leads to self education, self discovery, and sometimes healing.

What you want to avoid is what was stated above and becoming compulsive and having it turn into hypochondriacism on you.

Take care.