First of all I know this is biased but you sound like a mother and being a 17 year old diagnosed with ADD (very very similar to ADHD) it sounds like you are trying to cure them of some abomination. There is no way to "cure" ADHD. When someone has any form of ADHD, their minds are neurologically functioned in a certain way, which can disable slight portions of your child's brain but not to the great extent that many in the general public believe. The effects vary from case to case but typically some symptoms can include disorganization, faulty social skills (wanting to spend time alone rather than playing or quiet), being more prone to impulsivity, and many other possible traits. But there is no cure for ADHD, there are ways to help your child mentally, most of which are stimulants for the brain usually in methamphetamine form. But before you run and yell about giving your child drugs, there are many types of stimulants that help and all of which are in small dosages and not straight up methamphetamine. I take Concerta, which is a stimulant that does not require multiple-daily uses. Concerta is taken once daily and the drug is passed through the taker's system within the day and there are no remnants in one's body which prevents any risk of dependence. I would suggest you speak with your doctor about seeing a pediatrician who knows of a neurologist because he would know more than I would about the medications as well as the disease itself. The best thing to do for your child is, while they are growing up, be supportive when you recognize any behaviors that could relate to their disease and do not by any means punish them for it, it is beyond their control. It is a neurological disfunction which is usually passed down through genes. So your raising of them is not the cause. I really do hope you find what you can to best help your child.
At three years of age, I would not worry about it too much yet. It is extremely difficult to say a three year old actually has ADHD. A lot of the symptoms that could be ADHD could also reflect that they are simply a toddler. There are a lot of ways to deal with ADHD, especially at the age of three. It is a great time to help them learn some coping behaviors before they go to school.
My daughter has an issue with ADHD since she was young, but we have never medicated her. I am not against meds, but if they can learn to get through days without a negative impact and without relying on meds, then it is to their benefit. Rather you decide to go with meds or not, a focus on coping behaviors is pretty important.
At three, you can start teaching small things. If they are fidgety to the point of distracting everyone around them (which is actually pretty normal for any three year old), you can teach them to get it out by tapping on their leg. It is quiet, can be done under a desk, and is not overly distracting for those around them. When they start school, it is something they can do without drawing negative attention on themselves. You want to watch for energy buildups (again... can happen with any three year old), and give them constructive opportunities to burn it off. You would much rather see them running like a wild man on the playground than in your kitchen. If you know you have to go somewhere they are going to be sitting still, run some energy off of them first.
Get them some games that are fun, but that require focus. Try to get them to stick with them for as long as they can without causing them a lot of frustration. You can start slow, and work your way into more. There are many memory match games on the market with popular characters. Simple puzzles or other games where they are required to sit down and focus on detail will be helpful. Just be careful not to make them hate them by forcing it for longer periods than they can deal with.
If they are getting "too spazzy," help them bring it down a notch. At three, they won't be able to recognize when they are overly stimulated. It is up to you to remove them from the situation and find them a calmer situation and a focus.
Of course, keep talking to their doctor all the way through. Every case is different, but paying attention and finding alternative ways to cope with situations will always be useful.