As you learn more about your own subject, reading the textbooks will get easier. Are you familiar with different cultural academic conventions in texts? Knowledge on how texts are written offers insight into how they can be read more effectively. If your problem is difficulty with words, then you may have to actively work on your vocabulary range. Pay attention to key words that you come across in articles and learn them. Are you using a dictionary sensibly? Can you guess or infer the meanings of words? Do you know about skimming and scanning strategies? Expanding your vocabulary will help both not only with reading flow but also with remembering content. You could benefit from attending an academic reading course.