dude I don't know how you read it but when you do first thing you have to understand what you are reading otherwise nobody will remember what they read. Secondly, don't just read once you have to repeat it multiple times over the week and coming days. 
Try writing the stuffs in your own words about what you read. When you are reading make sure nobody is bothering you. 

May be padhesake pachey ram devko kapalvati garda samjhine shakti aaounthii ki

Dherai cholnu vayena, porn Ma dhyan diye pachi ka huncha.

dont study at all...be the last in class and fail in every subject to become like Bill Gates...lots of people give reason for not to study...so 

just an idea sir ji...

 vale bro,

remove all distractions like laptop, food, etc when you're studying. do not think about anything else, just keep your mind open for the stuff you read. if you start to think about some random stuff, stop studying. think about the random stuff for a minute or two, end it and go back to study. you'll hardly remember things you study when you're thinking about other stuffs. start with something small, like - study your chem book (or something else you need to study) for 15 minutes without any pause, focus just on the book. if you fail, try 10 minutes. if you succeed, bump it up to 25 minutes and so on. it's good to take a short break (2-5 min) every 45-60 minutes because there's only so much your mind can take.

in some cases, this issue of failure to concentrate is like a disease and taking drug helps. i can't remember what it's called, but I had a friend who had/has problems like yours. his doc pescribed him some drugs that help him concentrate. next thing, your "fight" with your wife did not cause this problem and neither did the head injury you had, unless it was a severe injury that hurt your brain, especially hippocampus area which is virtually impossible without hurting the overlying parts of the brain.
seems like the problem is more psychological than physiological, you should be able to fix it by yourself if you put in some serious effort.

 1) get pleanty of sleep. lack of sleep makes you forget things and can't concentrate.
2) read multiple times like someone said up there. hard work will get u to success.
3) what is it really bothering you? money, grades, love life, sex life, try to get a grip on the real issues rather than dealing with the symptoms. 
4) try mindfulness meditation at least 10-15 mins a day, look up online how to do it..will increase your concentration and you worry less..