Why i can not improve my level in English

[mokhtaro]

Essalam Alikom (May peace be upon all of you)
In the past, when i was a beginner in English, my level was improving in a fast way until I reached a medium level (I can write, read and communicate easily), but the problem I am stuck in the same level, I am not improving at all.
I know there are many people have the same problem
So the subject for debate is the following questions:

why i can not improve my level in English now?
or
Why i do not feel any progress in my English level?