Welcome to the forum, survivor05. The most important thing you should do at this point is to let go of that guilt. The fact that you went undiagnosed was not your fault. You could blame your mother, or the teachers, or any other adult who could have possibly identified your behavior as being consistent with ADHD, but the fact is that assigning blame will not change anything. Guilt is a useless waste of time.
So, having said that, your new life starts today. Live it looking forward, not backward.
You will not believe how freeing and how much of a relief it will be when you talk to your doctor and she tells you that your instincts are right and that you can do things to change your life starting now.
Best of luck to you, and don’t forget that all of us here are always willing to listen and offer advice. Most of us older ones have been where you are (some of us not so long ago, as a matter of fact). 