Посмотрите в энциклопедиях, учебниках или справочниках два понятия: linguistic performance (употребления языка) и linguistic competence (языковая компетенция) .
Возможно, в Вашем случае, преградой к общению на иностранном языке является недостаточно развитый навык употребления английского языка (linguistic performance), т. е. причины больше психологического характера. Причем, насколько я понял, навыки аудирования у Вас развиты, и проблемы возникают именно с порождением речи на английском. В этом случае можно порекомендовать только ПРАКТИКУ (аська, скайп, клубы любителей английского языка, выезды за рубеж) , а также ведение дневника на английском языке. Возможно, это не Ваш случай, но преградой также может быть и перфекционизм, излишняя строгость к себе и боязнь допустить ошибку. Естественно, всё это следует отметать как нецелесообразное.
Отрывок из Википедии "в тему":
"Linguistic competence is the system of linguistic knowledge possessed by native speakers of a language. It is in contrast to the concept of Linguistic performance, the way the language system is used in communication. The concept was first introduced by Noam Chomsky[1] as part of the foundations for his Generative grammar, but it has since been adopted and developed by other linguists, particularly those working in the generativist tradition. In the generativist tradition competence is the only level of language that is studied, because this level gives insights into the Universal Grammar, that generativists see as underlying all human language systems. Functional theories of grammar tend to dismiss the sharp distinction between competence and performance, and particularly the primacy given to the study of competence."
[Linguistic performance] "is also one of the two elements in Chomsky's performance-competence distinction, which relates to Language production (parole), with an emphasis upon how this is different from Competence, or the mental knowledge of language itself. Linguistic performance does not simply reflect the intrinsic sound-meaning connections established by the system of linguistic rules. It involves many other factors, such as extra-linguistic beliefs concerning the speaker and the situation play a fundamental role in determining how speech is produced, identified and understood. Furthermore, it is governed by principles of cognitive structure such as memory limitations, distractions, shifts of attention and interest, and errors (random or characteristic) that are technically not considered to be aspects of language."