Good morning and welcome. I have 6 (almost 7) year old twins, both with their own issues, but one, N, has just been formally diagnosed with ADHD and ODD. It is a constant guessing game as to what is the right action for that particular day, but hang in there. The group on this board have some wonderful ideas and have helped me a lot. I have found that in pretty much any situation, there is someone on here that has experienced it and can give advice or at least empathy. Just knowing that others are in the same boat is a tremendous help.
A great piece of advice that I found here is: Take time for yourself! This is particularly important if you are dealing with the child without support from a mate or significant other. You cannot be at your best for your child if you are totally worn out, physically, mentally, or emotionally. And these kids do drain us! Make sure to have some "pampering" time for you, even if it is just taking a nice quiet bath after little ones are in bed. And don't let yourself stop spending time with friends. I know for us, we stopped doing a lot of things that we used to do with others because of the twins behaviors, and that was a BIG mistake. We all need that adult time and normalcy.
OK I have rambled enough. Glad to have you here!