I agree with the PP - and that the only way you're going to know for sure is to have your DS tested by a qualified professional (ie not your general pediatrician). You should start by educating yourself more about ADHD and the appropriate ways to compensate. One of the good things about it is that even if your DS doesn't have ADHD, the skills you learn will still help him - the techniques are good for everyone. To start, you might think about looking at the CHADD website and find out when/where your regional chapter meets. They have free monthly meetings with a speaker (at least the NOVA chapter does) and I've learned so much from them
http://chadd.org/ . I've also found Ann Dolin's book Homework Made Simple to have useful techniques. If you look for it on Amazon.com, you'll also get some hits on other good books. The nice thing about Ann is that she's local and does presentations at a number of venues
http://anndolin.ectutoring.com/presentations/ at no cost to attend.
The attention issues you describe sound very familiar to me! I know how frustrating it can be. The good think is whether or not your DS has ADHD, you CAN teach him good study habits and routines which a lot of kids don't learn. He'll be so much better off. Good luck!