I am a mother of a 3 year old with ADHD and, though he is my first, I can tell you that learning about the disorder has changed my parenting style significantly. I used to subscribe to the "if I don't expose him to this or that, then he will never learn" and I would drag him to places and set him up to fail. One example is taking my son to a busy fast food restaurant with a built in playground right at noon. This was NEVER a good situation for him (or me) b/c it is just too much stimulation for him to handle. I have learned that there are just some things we cannot do and some places we cannot go until he gets older and more able to handle situations. I would tell you that what works for other kids as far as discipline and punishment does NOT work for my son. I had to adjust my way of looking at that as well.
We purused a diagnosis and currently have him on a supplement program. I am just not willing to put him on meds so early. I would encourage you to post this on the Parents of Children with ADHD section of this board. There are others like us who feel that our children have disorders and don't want to settle for "they are just like that because they are young" for an answer. You might also want to visit the Alternative Meds section of this board as well!
There is no harm in getting him checked. This doesn't obligate you to