Pronunciation and vocabularies

When I go to read a English book or a novel, the main and the only problem I get is vocabulary. Because when I go to read them I cannot always refer from the dictionary. So I do not know how to solve it.

Well I've got quite a high level of English, but I see from my students' experience that many find it difficult to actually start speaking it fluently, using the right words and collocations.

For me, the most difficult one is speaking. When I try to talk, I don't know any words , and I feel like my brain is empty.Even I somehow manage to think about something to talk, there is no sound, it feels like the words stuck in the throat and sound doesn't come up.

To me the most complex one is to pronounce the consonants and vowels in certain situations like when i have to pronounce "a" as in apple, or in ant, or in bar, simply the phonemes that fall under the "a" sound. Or take anyother consonant. Although i know the IPA and have enough knowledge about the phonetics but still this is a huge obstacle in my way of learning.