Everyone experiences the learning plateau when learning a new subject, and it is specially true of language learning. Starting from zero, you make progress that you are aware of. It's a good feeling, but there comes a point - the "plateau" - where you begin to feel that, for all your efforts, you are not making the progress you made at an earlier stage. You are making progress, but there are several reasons why you have this negative feeling.
First of all, you are no longer dropping pieces of vegetable into a clear soup, where you can see every piece. You are adding pieces to a soup that has changed from a bouillon to a minestrone, so it's very difficult to separate the new bits from the old bits.
Secondly, it is much easier to devise tests which measure progress at lower stages of learning. It is no problem to separate, say, a beginner from an intermediate student, but much more difficult to devise test mechanisms which will distinguish, say, a good student from a very good student.
As this is a deeply boring subject, I will stop now, and ask you just to pause and admire Ebru's English Language Soup before going on to something more exciting, whatever that may be.
PS Today, I found out that I was a Rat. Funny how you can go through life ignorant of important truths about yourself!