I haven't been diagnosed with ADD either, although I scored 70 on the quiz for that on this site. I have symptoms like not noticing things, and even spacing out when somebody is talking such that they get finished and I have no idea what they said. My depression the past year made it impossible to concentrate on reading too. I would get down to the bottom of a page and not have a clue what was on that page I just read, so I had to re-read, and it took like 10 times to get through a paragraph or a page. And I was a full-time student for the past year. I made it through and got straight A's.
A lot of what I did was just to work really hard at getting my reading done, even though it took all of my effort. I knew how much reading I needed to get done by when, so I divided it up into how much I had to finish each day. When reading, I used an index card to push my eyes down the page. I place the card above what I have read, as I learned in a speed-reading class that our eyes tend to follow a pattern where they go across the line and then up and back to the next line, but they don't go down below much into unfamiliar territory. So covering above the line you are reading helps keep your attention there. Also, stop frequently and ask yourself what the topic and main points are. Pay particular attention to chapter headings, section headings, etc. and look through the chapter and look at the pictures, captions, charts, etc. before reading and also after to review.
Getting the information in more than one mode helps me too. If you can get an audio recording of the text, listen to it as you read. I have read my text books in class, following along as the instructor lectures. Found out that one of them, years ago, was basically just reading straight from the book, which worked out for me since I had carpal tunnel syndrome at the time and couldn't take notes, so I underlined what he said as he went.

Some will give you an outline of their lecture in advance so that you can take notes and fill in on that outline. That helps a lot.
Another thing that doesn't always make sense to everyone, but works for me, is to have something for my hands to do while I'm listening. I knit during class. Doodling can help too. I even knit while I'm reading (using something like a music stand to prop up the book). Since I'm a tactile learner, it helps to have my hands busy. I also know how to fingerspell, and I fingerspell what I hear, but had to stop doing that because they didn't understand why I was doing it and thought it looked to strange.
Good luck! I know you can do it!
<font color=orange>"Never forget: 2 + 2 = 5 for extremely large values of 2."</font color=orange>
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“We should always pray for help, but we should always listen for inspiration and impression to proceed in ways different from those we may have thought of.”
– John H. Groberg