It's not your fault...

To speak English fluent, you need to think in English, however you've been practice over 3 years and you still have many difficulties to speak, even tough you are able to understand fluently, however you can't speak anything, perhaps your shame are one of the main barrier. You getting start to take course and after that you give up once more. Over twenty years practice English by myself let me sharing my own experience, don't worry about mistakes, they are common, in particular for beginners, don't limit only practice English during the course (There are many great schools spread around Brazil), studying hard, at least, getting start 30 minutes a day, using the internet, skypes, msn, orkut's community or shedule with friend to study English. You don't realize how much is difficult studying by yourself, I did that for many years, and right now I'm studying English with a great staff of professionals, but if you don't have any conditions there several ways to improve and study English, great onlines courses. Never give up your dreams, keep practicing, keep studying, the more you do that, more you learn asap.