Well my son has ADHD according to the psychiatrist and also Aspergers. My husband is undiagnosed ADHD and I am pretty sure my 3 year old has ADHD but as you say too young for much intervention at the moment.
My eldest as a child was a mixed bag which is why I question the ADHD diagnosis and think it could be just Aspergers. As a small child he was hard work, he wouldn't go to bed, spent most of the night awake and walking round the house, he was up at the crack of dawn, he used to run off all the time in any direction. He could sit and watch a film he really liked all the way through though or really concentrate on books or jigsaws. He was fully potty trained at 2.
As he got older he settled down but he still can not sustain attention in most areas unless it is something he enjoys. He lays awake until late at night as he can't sleep, he wakes up early.
DS2 who is 3 I have no doubt has ADHD, as a baby he never slept, in the bath he used to kick his legs from birth, so fast and hard like a machine the whole time he was in there. He won't go to bed either, wonders the house at night, doesn't and never has napped even as a baby, doesn't play with toys, can't sit through one page of a book with out jumping up, can't sit at a table for a meal, runs off everywhere all the time he wont even start potty training yet. It is hard to imagine but his energy level and inability to sustain ANY attention to anything other than Mr Tumble is much more than the normal toddler level. But you always find people who say it is normal.
If nursery are noticing it too then the HV can refer you to camhs, we are just waiting to see how my 3 year old gets on at new playgroup and if they have the same concerns the HV will refer him, she already said she will but yet again it is that thing of they will probably just 'watch and wait' due to his age.
I know how you feel though it is so frustrating to not get any help and it is so hard. Coping becomes difficult as the normal methods of dicipline aren't effective as adhders don't learn from them. The way the specialist told us was that an instant reward system was better for someone with ADHD but this was when dealing with my 9 year old?
Which part are you struggling with most? Is it the endless energy or sleep etc? It is also a misconception that kids with ADHD are badly behaved as usually they aren't but can get that way when they are older as they are lead to believe they are bad and tend to begin to believe it. Also the majority are very bright, so long as they are doing something that interests them. I don't know if I have been of any help but I am here if you would like any advice a chat xx