You are you, and you'll be still be you after a diagnosis.  It's a a diagnosis, not a test that you have to 'pass'.  You aren't applying for a job or trying to join a team.

Your mindset - 'will they  believe me?' - is based on a misunderstanding.  A diagnosis is really not a question of whether anyone believes you.  Don't try to 'convince' the diagnostic team of anything - that amounts to an attempt to skew the diagnosis, and there's no point in you receiving a skewed diagnosis.  Just be honest.

It's a totally dispassionate process.  If you aren't autistic but you feel different there may be something else that applies to you, and you should know.  Knowing allows you to navigate the world more successfully.   

Whether you are, or not autistic, wishing you all the best and hope you learn something about yourself.

PS - if you're doing this through the NHS, stand by for a very long wait.  

Try this book - it's only £3.50 on kindle/ipad etc from Amazon

If you are autistic, your brain works in a different way from other people who are not autistic. Just like your sexuality, or your skin colour, it's how you are born.  Some autistic people do need support to help them with certain things, but not all autistic people. autistic doesn't mean you have a disease, so there's no need to feel scared about having an assessment.

As for the assessment, they don't attach you to a lie detector, or strap you to a share and shine a light into your face. It's a very gentle process of being interviewed by a trained clinician, who has read all the data provided about your childhood and then during an interview, observing your reactions and responses to their questions. They are not there to believe or disbelieve you. They are there to observe and record your responses and match them up with their diagnostic criteria.

Just from reading a lot of posts on this forum I've learned that a lot of people diagnose themselves as autistic long before they go for an actual assessment and this can cause them a lot of stress and anxiety because they are afraid that their own diagnosis won't be confirmed. But the converse is also true where many people go for an assessment convinced that they are not autistic and get anxious about receiving a diagnosis (as is the case for me).

There really is no answer to this only to go into an assessment without any expectations or biases, and recognise that you can't predict the future, and when the future arrives as the present, whatever the outcome of the assessment, you will deal with it there and then.

If you click the link below, it will take you to the National Autistic Society (NAS) information pages.

advice-and-guidance/topics/diagnosis

There is also some unusually useful information on the NHS website. Strange though it may seem, this is one of the few areas in the Greater Manchester area where the NHS have competent and reasonably supportive clinicians in post.  But it may be different depending on where you are in the UK. 

www.nhs.uk/autism

Hello!  I'm new to this site, too, and went through a similar dilemma recently when I realised I was probably autistic.

Have you done much research about it?  I can only speak from my own experience, so it may or may not be helpful to you, but I found that reading books and blog posts by other autistic people was really useful.  Reading about their experiences triggered (in a good way) memories of things that happened in my own life, which I've noted down to use when (if) I have an assessment.  (Have been referred by GP and waiting to hear if I've been accepted for one.)