I was diagnosed more than ten years ago, when I was 32, so hopefully I can be of some help here. My diagnosis was Asperger's, now HFASD (a term I don't agree with, but that's an argument for another day).
I will be honest and say I didn't suffer terribly with masking as a young person, because I had the great good fortune to grow up in a supportive family (many of whom are or almost certainly were autistic - we're an Aspie family!) and a very nurturing school environment, and I was comfortable 'embracing my weirdness' from an early age.
Things really only got difficult for me when I was in my mid-late 20s / early 30s and interacting with far more NTs at work and so on than I had previously been used to - in fact, that's what prompted my journey to diagnosis.
However, I do probably continue to mask to an extent, particularly when dealing with 'normal life' (tradespeople, at the supermarket, at work to an extent - I am a senior subject matter expert at director level).
I cope with this by having 'safe zones' and 'safe people' - my OH, my best friend, my sister, all of whom understand who I am. They have no issues with me coming home and walking straight past them to sit in a darkened room for two hours / quietly stimming away in front of the TV / talking about whatever this month's special interest is for hours.
Unfortunately, I think an element of masking is inevitable for most ND adults with the capacity to 'function', as we live in a world built by and designed for NTs. It's important to recognise this and I feel diagnosis is, for many people, the first step in unpicking who they are.
That said, it is a long process - some people talk of a 'lightbulb moment' on diagnosis, but there is no guarantee: like grief, it's not linear and it will take some people longer than others. I, for example, was essentially constantly angry for about two years post-diagnosis.
I also did a HUGE amount of reading - academic studies, medical research, books and papers written both ND and NT people - which helped me, because I am process-driven and seek 'rules'.
Ultimately, be kind to yourself and give yourself time.