Firstly, your written English is very good. Something tells me that you are trying to read materials that are just a little too complicated for you. I find that the same happens to me if I read Japanese that has more complicated grammar, or too many words that I do not recognise.
What happens if you read simpler materials? Do you understand it all? Perhaps using some graded reading materials would help?
In the UK, we have many graded reading books that allow you to choose a level of English to suit your reading level. Oxford University Press has many such books available. Their website is https://elt.oup.com and I imagine there are other web sites that may offer such reading materials for free, if you search for them.