I was diagnosed spring 2016 and started on sinemet immediately. I phoned DVLA and they sent me a form to fill in. I was given a 3 year licence, which I believe will be renewed unless I have a drastic change. They know I take sinemet &it made no difference. You should also notify your insurers. They can't refuse to insure you.
Sinemet works for me, it's not a magic bullet, it won't put you back to where you were before but it helps.
Having PD takes some get used to but it's not the end of the world even though that's how it feels initially. I find this forum helps me get it more in perspective. Just pick & choose to read what suits you. D