Rabbit, I think you're being too tough on yourself.  You express yourself quite well in English.  Perfect?  No.  Quite well?  Definitely. 

(Let me add here that everyone makes mistakes from time to time, I don't care who they are.  I bet Luiz Verissimo screws up in Portuguese from time to time.  Hey, it happens.

There are people in this Forum who love to pounce on mistakes.  Maybe it makes them feel superior.  I really don't know.  It's sad.)

When you are back in Brazil, try to find a native speaker to hang out with.  The every day vocabulary you will learn is going to set you apart from others.  Nothing wrong with a sleeping dictionary. 

And lighten up!  I think you're doing a great job.