I have heard two suggestions that should help you:
(1) Learn on your own, without a teacher. Various software tools may help, like Anki. Public education and its texbooks are *extremely* inefficient for many reasons I won't go into, unless you want me to. The main exception about learning on your own is that a teacher is particularly useful for learning proper pronunciation, but online software tools can help there, too.
(2) At least you are aware that your main deficiency is vocabulary. Remember that no one in any language, even their own native language, learns every word. Think of learning vocabulary as in infinite chore you can never complete. Vocabulary is the most important part of language learning, more so than pronunciation, script, spelling, or grammar, because if you know the words you can communicate somewhat, even if the words are in the wrong order or pronounced wrong. The following guy has a radical solution, but it takes a lot of work, and it is unwise to memorize the vocabulary for an entire book, but for an entire chapter or entire page I believe he has good advice:
Learning Languages: ADVICE NOBODY WANTS TO HEAR.
Sep 21, 2018
à-bas-le-ciel
The minimum amount of vocabulary you need to begin to get by comfortably in any language is in the 2,500-3,000 word range. I have many references for this, which I can provide, especially if I can attach a document here, if you want. In short, learning a language is a *lot* of work, and should not be undertaken lightly if you intend to speak and understand it well. The vocabulary takes the most time to learn, but the grammar takes the most intellectual effort to learn. Ideally you should learn the pronunciation before anything else, even before you learn a language's alphabet, but most people don't do that, even though pronunciation can be learned in a matter of weeks and will speed up the learning of everything else.
Here's one guy who learned how critical a large vocabulary is, when he took a crash course in Spanish:
Spanish in a Month - Learn Spanish Documentary
Nov 30, 2015
Connor Grooms
This polyglot also emphasizes the need for learning a lot of words:
Learn Vocabulary Fast
May 14, 2018
Steve Kaufmann - lingosteve