Hello, Ms. B: I think that it might be better to say: Why can't I speak English? (Remember: We ALWAYS capitalize the word "English.") How can I write correct English? How can I write English correctly? How can I write grammatically correct English? ***** In English, there is this saying: PRACTICE MAKES PERFECT. (That is, the more you do something, the better you become.) You speak your native language correctly. Right? Why? Because you have used it since you were a child. Well, you can also speak English correctly. You just need to practice it and to give yourself time. You also need to read and listen to English on a regular basis. Little by little, your understanding of English WILL improve. Of course, the only way to REALLY become fluent is to work or live with native speakers.

after successful finishing a couple of good textbooks

Are you following a english course in your city? What are you doing for learning english?