this answer is going to sound extremely generic, but the truth of the matter is, you just have to keep on reading and practicing.
I was horrible at reading comprehension. I'm not a native speaker and just like you, can lose concentration easily. But since I started to prep for GMAT, I've really begun to read a lot of different stuff, including both intelligent materials, such as Economist, the financial news online, and non-intellectual materials, sports magazine and celebrities-related materials. On top of all the reading, I practiced a whole bunch of reading comprehension materials and for some odd reason, the eureka lightbulb just turned itself on on top of my head. I started understanding exactly what the question is asking; I started understand the gyst of the passage; I started doing better on reading comprehension. Of course, I'm not getting 100% right, but I've definitely boosted from just a 30-50% correct to a 60-75% right, depending on the passage itself, the range could be even higher. So don't give up! The best way is to simply keep practicing!!