Stay motivated

( The way you have worded the sentence, I thought you meant physical exercise. But now I have realized you meant to say exercise as in your studies.) *So the best thing to do to prevent confusion would be to choose a different word or  not use the word "exercise" at all.*

 I have to face  a lot of concept and complex grammar so that it is difficult to keep on it. I had encountered many complex concepts in English grammar.  

I had been struggling with a grammatical topic for  approximately three weeks. I had noticed my level of English was not high. I was not motivated and my level of interest began to decrease.

I have found that I have not high level motivated like begin,my interest start to decrease.

With this in mind, I had decided to look for help by asking my friend who is an native English speaker. My friend provided me with advice about how to stay on track with language learning, as well providing me with advice on overcoming tough situations. She said that you should divide your study into four part: words, grammar, listening and writing. The most important study of English for me is writing.

 to my friend who English language level is very well. After understanding of the situation ,She comes up with some advice to help me to overcome(through)trouble and get back on stack with language learning. She suggest that study is divide into four parts:words ,grammar,listen,writing. One of the most important is writing for me .(When the input of words and grammar reaches to a certain extent ,the output of writing could improve using skills and check questions) * This is a good comparison*

We frequently communicate with others in English. I am agree with my friend ,and I plan to write a short paper every week.

Fighting!