Ok go to your GP and ask for a referral to CAMHs for an assessment. You will need to tell the GP your symptoms and how you feel it is affecting your life. It may be good to take your Mum with you (age dependent). I am very surprised it has not been picked up whilst you are at school. How old are you?
No but seriously go to your GP to get a proper diagnosis.
The first you do is go and seek help to an adhd expert to get you diagnosed. Pretty sure they will help you to make you at ease. I recommend this adhdcentre.co.uk this centre is really amazing base from my relatives who just went there. So good luck and god bless.