It sounds like it can be ADD. The actual term for it now according to the DSM-IV which is the diagnostic manual used by psychologists. ADHD can take many forms and may or may not include hyperactivity. My son and I and probably my dad have ADHD. I am 30 and while I have had the symptoms all of my life, It really started to interfere with work when I got a job as a bank teller and had a real hard time focusing on my work, and multi tasking.
In school I always had a hard time focusing, and even now in college I have a hard time not daydreaming. People get frustrated when they are talking to me sometimes because they will be halfway through a story and i will be like "who are you talking about?" And it appears that I wasn't paying attention even though I was trying to.
Some drugs like Concerta and Adderal are useful in treating ADHD, and I have been on them in the past, but due to finances I am currently not taking anything and am for the most part managing just fine.
I have heard ADHD described as if your brain were "blinking." Imagine if you were reading a book and every 5 or so words you blink for a second or two. You would miss some of the words and some of the context and meaning of what you are reading. The same is true with ADHD. We tend to miss some things, which can be awfully frustrating and sometimes embarrassing. You can learn to train your brain to fill in the missing pieces enough to where you can figure out what you missed.
It seems like you may have ADHD, but see your doctor for an accurate diagnosis. Once and if you realize that is what you have and learn a little bit about it, things will start to make a little more sense. You will start to understand yourself better. How old are you. Whatever the age it is good to understand and learn to deal with ADHD.
You should realize that ADHD doesn't make you as the book says "lazy, stupid, or crazy." However that is sometimes how we feel, or may be labeled by others. You just have a brain that works differently and once you learn those differences you can adapt rather well. There are things about the way I think that are different, but usually I come up with a new spin on things that someone else may not have thought of. This helps at work and at school. As a sort of writer, I am not a great speaker, but can write well, because it gives my brain time to organize my thoughts.
Check out these websites for a lot more help and information. Good luck and feel free to let me know how everything goes for you:
Attention Deficit Disorder Association (ADDA)
www.add.org
Children and Adults with Attention Deficit Disorder (CHADD)
www.chadd.org
ADDitude Magazine
www.additudemag.com
ADDvance
www.addvance.com