Hi Pavel,
I´m not sure if I understood what your problem is. I think that you must persevere, though. Language learning is never easy and it never goes smoothly. It depends of a lot of try and error, repetition and massive exposure to the language.
I am learning French right now and I am facing a lot of trouble in doing so, despite the fact that my native language (Portuguese) is also a Latin language. I keep forgetting obvious words, committing mistakes and sometimes it seems that I will never be capable of understand native speakers talking.
However, I know for a fact that it will eventually get better and while this does not become true I just keep going and try to have a good time.
If I were you, I would just try to adjust my expectations about the learning process to a more realistic level, don't be too hard to myself, persevere and, most importantly, I would try to strength my personal bond to the language (in other words, I would try to LOVE the language and things that are related to it), so I can have a good time while learning.
Keep in mind that forgetting words and committing mistakes are normal. It happens to everyone. If that were not happening to you, then you should be concerned.
Hope this helps you. Good luck!