My cousin, who is an adhd nurse with 20 yrs experience, passed on lots of suggestions to me when I had problems with ds1, but the most important one seems to be:
Set up consistent behaviour management with dp/dh and also with the school so all adults are clearly working together.
This resonated with me as my dh is Italian and had completely different ideas about child rearing. It took us years to work out a compromise - our own way of doing things, but since then things have been much better.
For me this translated to:
Decide on a bedtime routine/time and stick to it
(ds1 hadn't slept all night without waking since he was born - this lasted until he was 7, now he's ok).
Make sure they get plenty of outdoor exercise. For me again, this meant walking 20 minutes to school and back instead of getting in the car. People would frequently stop us and offer lifts and seem horrified if we didn't accept thinking I was tiring him out, but honestly, he needed to run off the energy! I also did more park visits (which I hate).
Cutting tv down a lot has helped too. I now allow both my ds's (younger one is 4) a maximum of an hour on the evenings on which they have no other hobbies (maybe 2 or 3) and they don't watch any tv at all before school or just before bedtime.
And you need a good relationship with the school, which can be a challenge - depends on the school. I had to literally insist on extra meetings with ds1s teacher (who didn't want to know as ds1 wasn't a problem as such, but things were not right either)so that we were all in agreement.
But havingproblems, you have all my sympathy. Some children have so much more energy - can be difficult if, like me, you are knackered all the time from working, cleaning, organising kids, dh, friends, school pta etc etc etc and everything else we mums have to do. Good luckxxx - my cousin also said that nearly all the adhd children she worked with were really bright! If their energy is harnessed correctly, who knows, you could have the next prime minister on your hands, (or similar position that requires boundless energy, not sleeping at night and intelligence)....