English is my native language and there were still some of the harder, more scientific, RC passages that I read several times without really understanding what they were saying!
One of the tips given in the various books is to write down, in your own words, the thesis of the passage as well as the main ideas of each paragraph and the conclusion. I think that this has worked for other people as it helps you to pick out the pertinent information. I hope it goes better for you!