Having read a piece, it may be advantageous to analyse how you actually felt not about the work itself, but about reading the work. Were you able to sit comfortably and digest without interruption? Was there a need to move to somewhere else while you were in the middle of it? Did you find your mind wandering even though you were looking at the book all the time? All of these can affect how you study and it may be good to address and “fix” some of them.
Personally I find with the empty house I can slip downstairs sit in the front room and if cold put the fire on. I am left with what will be a good amount of uninterrupted time to then understand what I am reading.
There have been times when the radio has been on or someone has been in the room that causes me to be slightly distracted. The radio, more than anything causes trouble, as often music will end and a DJ will start his monologue. Turning the damned thing off or putting on a CD without the DJ easily repairs this. Asking someone if they would mind being a bit less noisy could also is helpful, if it does not cause tension.
It would seem that the less distractions there are and the less opportunity for distraction, the more focused one can be. More focus may well lead to an easier understanding of what you are reading. If it is the case that you are uncomfortable where you are studying or sidetracked, a change to where and perhaps how you are going about it may be of advantage to you.