The intermediate plateau is a difficult level and many people stop learning when they reach it. Try to make opportunities to speak to other English speakers, even if they aren't natives. Look for English clubs in your area. The key is to activate the language and try to speak for as long as you can. That's the best way to push yourself to improve your speaking skills because studying grammar rules will not help you speak better. Talk to yourself in English, think in English, write in a journal in English, but use the language. Isolate your problem areas and that will help you fix them more effectively. Just keep practicing and don't give up. You can push through the intermediate plateau.

Abby said pretty much all so I won't have much to add. Challenging yourself is definitively the right attitude to adopt if you want to make significant progress. Language learning is all about immersion (at least this is how I manage to become proficient). Just make sure to use adapted material because if it’s too hard you’ll just get frustrated, but you shouldn’t shy away from more advanced material either, it’s just a question of balance. Anyway, I’ll be available whenever you need. All the best to you, and don’t give up :).