My problem learning a new language of programming

My first language of programming was C, my second language of programming was Pascal and the last Visual Basic, Java.

I learn this language of programming in the university, i learn the basic of this language. The time for learn this language was weeks and develop a project at the end of the course.

When i want learn a new language of programming my learning curve is slow. I start the first month of the year very well but i have insomnia, discouragement and loss interest to month or the last week of the month.

So, i am unstable. At the end i don't dominate the language and waste time.