How to keep track of appointments and events?

Hi everyone. I am a 24 year old single mum with a 4 year old son. I have adhd. My son starts primary school in September and I am stressed about remembering appointments and events etc. I am extremely forgetful and I struggle to keep track of things. I’ve tried putting notes in my phone, keeping a diary, keeping a calendar on my fridge and none of those have been successful to me. I either forget to write them down in the calendar or I forget to check the calendar. Now that he’s going to be in full time education and the fact that he is on the pathway for autism, has a speech delay and additional needs, I really want to do the best for him and keep track of everything going on. Has anyone else struggled with this and found something that works or even if it did not work for you is there something I could try that I haven’t yet? TIA