Too big of a vocabulary

I find that I have a very large sufficient vocabulary, however my grammar is not good, especially when I speak. I find it difficult to put together senteces correctly even if I know every word. Also I often find myself wondering what word to use, because I know many synonyms for the same word, it would often be easier if I only knew one.

Do you think it's possible to have the vocabulary too large for your level? How to ammend this problem?

what you need to improve is your stock of lexical blocks, not individual words.
Lack of speaking practice is also a siginificant factor for your incompetency.

I think the more vocabulary you have the better. You just need to listen more.

Many words are only used in specific situations or even expressions.

No. You can't have too big of a vocabulary. lol