If you continue to find it difficult, keep it aside for a day. The next day, read the portion again. Note down any new points that come to mind. If it's convenient ask someone else to read out the points to you while you are in a relaxed mood. Re-calling the previous' day's portion is a technique of familiarizing yourself to the subject matter and you will find that tension about that subject will gradually decrease.
Recitation is a very old method of learning and proves to be useful.
This is because reading out in a rhythmic manner causes changes in the brain. This is why it is easy to learn songs or advertisements because the mind is inclined to remember a rhythm rather than monotonous reading. Many times we become very disheartened when our efforts in studying do not pay off. Many of us can identify with the above characteristics. We need to have fixed timings for everything .