Yes, it is a matter of practice. I would recommend that you set aside a specific amount of time each day to focus on enriching your English vocabulary, grammar, and speech. Are you surfing the Internet for sites that are written in English, or have streaming video in English? Visit sites that contain magazine or newspaper articles. Watch streaming video clips of current events. Select a few songs that you enjoy listening to and then find the lyrics online. Locate an online pen-pal that is agreeable to being a mentor.
'I realized that when I speak I always use the same words (the ones I'm comfortable with) and make the same mistakes.'
What 'mistakes' are you making... and, if you know they are mistakes, what are you doing to correct them?
Finally, a gentle reminder for you: The word English is always capitalized (never 'english') when you are referring to the English language.
I hope you will write us, again! Practice, practice, practice!!!
Student or Learner